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Table Of Contents
ip forward-protocol spanning-tree
ip forward-protocol turbo-flood
ip verify source vlan dhcp-snooping
IP Addressing Commands
Use the commands in this chapter to configure and monitor IP Addressing.
clear host
To delete hostname-to-address mapping entries from one or more hostname caches, use the clear host command in privileged EXEC mode.
clear host [view view-name | vrf vrf-name | all] {hostname | *}
Syntax Description
Command Default
No hostname-to-address mapping entries are deleted from any hostname cache.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
This command clears the specified hostname cache entries in running memory, but it does not remove the entries from NVRAM.
Entries can be removed from the hostname caches for a DNS view name, from the hostname caches for a VRF, or from all configured hostname caches. To remove entries from hostname caches for a particular DNS view name, use the view keyword and view-name argument. To remove entries from the hostname caches for a particular VRF, use the vrf keyword and vrf-name argument. To remove entries from all configured hostname caches, use the all keyword.
To remove entries that provide mapping information for a single hostname, use the hostname argument. To remove all entries, use the * keyword.
To display the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views, use the show hosts command.
To define static hostname-to-address mappings in the DNS hostname cache for a DNS view, use the ip host command.
Examples
The following example shows how to clear all entries from the hostname cache for the default view in the global address space:
Router# clear host all *The following example shows how to clear entries for the hostname www.example.com from the hostname cache for the default view associated with the VPN named vpn101:
Router# clear host vrf vpn101 www.example.comThe following example shows how to clear all entries from the hostname cache for the view named user2 in the global address space:
Router# clear host view user2 *Related Commands
clear ip route
To delete routes from the IP routing table, use the clear ip route command in EXEC mode.
clear ip route {network [mask] | *}
Syntax Description
network
Network or subnet address to remove.
mask
(Optional) Subnet address to remove.
*
Removes all routing table entries.
Defaults
All entries are removed.
Command Modes
EXEC
Command History
Examples
The following example removes a route to network 10.5.0.0 from the IP routing table:
Router> clear ip route 10.5.0.0ip address
To set a primary or secondary IP address for an interface, use the ip address command in interface configuration mode. To remove an IP address or disable IP processing, use the no form of this command.
ip address ip-address mask [secondary [vrf vrf-name]]
no ip address ip-address mask [secondary [vrf vrf-name]]
Syntax Description
Command Default
No IP address is defined for the interface.
Command Modes
Interface configuration
Command History
Usage Guidelines
An interface can have one primary IP address and multiple secondary IP addresses. Packets generated by the Cisco IOS software always use the primary IP address. Therefore, all routers and access servers on a segment should share the same primary network number.
Hosts can determine subnet masks using the Internet Control Message Protocol (ICMP) mask request message. Routers respond to this request with an ICMP mask reply message.
You can disable IP processing on a particular interface by removing its IP address with the no ip address command. If the software detects another host using one of its IP addresses, it will print an error message on the console.
The optional secondary keyword allows you to specify an unlimited number of secondary addresses. Secondary addresses are treated like primary addresses, except the system never generates datagrams other than routing updates with secondary source addresses. IP broadcasts and Address Resolution Protocol (ARP) requests are handled properly, as are interface routes in the IP routing table.
Secondary IP addresses can be used in a variety of situations. The following are the most common applications:
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There may not be enough host addresses for a particular network segment. For example, your subnetting allows up to 254 hosts per logical subnet, but on one physical subnet you need 300 host addresses. Using secondary IP addresses on the routers or access servers allows you to have two logical subnets using one physical subnet.
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Note
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To transparently bridge IP on an interface, you must perform the following two tasks:
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To concurrently route and transparently bridge IP on an interface, see the bridge crb command.
Examples
In the following example, 131.108.1.27 is the primary address and 192.31.7.17 and 192.31.8.17 are secondary addresses for Ethernet interface 0:
interface ethernet 0ip address 131.108.1.27 255.255.255.0ip address 192.31.7.17 255.255.255.0 secondaryip address 192.31.8.17 255.255.255.0 secondaryIn the following example, Ethernet interface 0/1 is configured to automatically classify the source IP address in the VRF table red:
interface ethernet 0/1ip address 10.108.1.27 255.255.255.0ip address 11.31.7.17 255.255.255.0 secondary vrf redip vrf autoclassify sourceRelated Commands
ip broadcast-address
To define a broadcast address for an interface, use the ip broadcast-address interface configuration command. To restore the default IP broadcast address, use the no form of this command.
ip broadcast-address [ip-address]
no ip broadcast-address [ip-address]
Syntax Description
Defaults
Default address: 255.255.255.255 (all ones)
Command Modes
Interface configuration
Command History
Examples
The following example specifies an IP broadcast address of 0.0.0.0:
ip broadcast-address 0.0.0.0ip classless
To enable a router to forward packets, which are destined for a subnet of a network that has no network default route, to the best supernet route possible, use the ip classless command in global configuration mode. To disable the functionality, use the no form of this command.
ip classless
no ip classless
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Usage Guidelines
This command allows the software to forward packets that are destined for unrecognized subnets of directly connected networks. The packets are forwarded to the best supernet route.
When this feature is disabled, the Cisco IOS software discards the packets when a router receives packets for a subnet that numerically falls within its subnetwork addressing scheme, no such subnet number is in the routing table, and there is no network default route.
Note
Examples
The following example prevents the software from forwarding packets destined for an unrecognized subnet to the best supernet possible:
no ip classlessip default-gateway
To define a default gateway (router) when IP routing is disabled, use the ip default-gateway command in global configuration mode. To disable this function, use the no form of this command.
ip default-gateway ip-address
no ip default-gateway ip-address
Syntax Description
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
The Cisco IOS software sends any packets that need the assistance of a gateway to the address you specify. If another gateway has a better route to the requested host, the default gateway sends an Internet Control Message Protocol (ICMP) redirect message back. The ICMP redirect message indicates which local router the Cisco IOS software should use.
Examples
The following example defines the router on IP address 192.31.7.18 as the default router:
ip default-gateway 192.31.7.18Related Commands
ip directed-broadcast
To enable the translation of a directed broadcast to physical broadcasts, use the ip directed-broadcast interface configuration command. To disable this function, use the no form of this command.
ip directed-broadcast [access-list-number | extended access-list-number]
no ip directed-broadcast [access-list-number | extended access-list-number]
Syntax Description
Defaults
Disabled; all IP directed broadcasts are dropped.
Command Modes
Interface configuration
Command History
Usage Guidelines
An IP directed broadcast is an IP packet whose destination address is a valid broadcast address for some IP subnet, but which originates from a node that is not itself part of that destination subnet.
A router that is not directly connected to its destination subnet forwards an IP directed broadcast in the same way it would forward unicast IP packets destined to a host on that subnet. When a directed broadcast packet reaches a router that is directly connected to its destination subnet, that packet is "exploded" as a broadcast on the destination subnet. The destination address in the IP header of the packet is rewritten to the configured IP broadcast address for the subnet, and the packet is sent as a link-layer broadcast.
The ip directed-broadcast command controls the explosion of directed broadcasts when they reach their target subnets. The command affects only the final transmission of the directed broadcast on its ultimate destination subnet. It does not affect the transit unicast routing of IP directed broadcasts.
If directed broadcast is enabled for an interface, incoming IP packets whose addresses identify them as directed broadcasts intended for the subnet to which that interface is attached will be exploded as broadcasts on that subnet. If an access list has been configured with the ip directed-broadcast command, only directed broadcasts that are permitted by the access list in question will be forwarded; all other directed broadcasts destined for the interface subnet will be dropped.
If the no ip directed-broadcast command has been configured for an interface, directed broadcasts destined for the subnet to which that interface is attached will be dropped, rather than being broadcast.
Note
Examples
The following example enables forwarding of IP directed broadcasts on Ethernet interface 0:
interface ethernet 0ip directed-broadcastRelated Commands
ip forward-protocol
Specifies which protocols and ports the router forwards when forwarding broadcast packets.
ip forward-protocol
To specify which protocols and ports the router forwards when forwarding broadcast packets, use the ip forward-protocol command in global configuration mode. To remove a protocol or port, use the no form of this command.
ip forward-protocol {udp [port] | nd | sdns}
no ip forward-protocol {udp [port | nd | sdns}
Syntax Description
Defaults
Enabled
Command Modes
Global configuration
Command History
Usage Guidelines
Enabling a helper address or UDP flooding on an interface causes the Cisco IOS software to forward particular broadcast packets. You can use the ip forward-protocol command to specify exactly which types of broadcast packets you would like to have forwarded. A number of commonly forwarded applications are enabled by default. Enabling forwarding for some ports [for example, Routing Information Protocol (RIP)] may be hazardous to your network.
If you use the ip forward-protocol command, specifying only UDP without the port enables forwarding and flooding on the default ports.
One common application that requires helper addresses is Dynamic Host Configuration Protocol (DHCP). DHCP is defined in RFC 1531. DHCP protocol information is carried inside of BOOTP packets. To enable BOOTP broadcast forwarding for a set of clients, configure a helper address on the router interface closest to the client. The helper address should specify the address of the DHCP server. If you have multiple servers, you can configure one helper address for each server. Because BOOTP packets are forwarded by default, DHCP information can now be forwarded by the software. The DHCP server now receives broadcasts from the DHCP clients.
If an IP helper address is defined, UDP forwarding is enabled on default ports. If UDP flooding is configured, UDP flooding is enabled on the default ports.
If a helper address is specified and UDP forwarding is enabled, broadcast packets destined to the following port numbers are forwarded by default:
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Examples
The following example defines a helper address and uses the ip forward-protocol command. Using the udp keyword without specifying any port numbers will allow forwarding of UDP packets on the default ports.
ip forward-protocol udpinterface ethernet 1ip helper-address 10.24.42.2ip forward-protocol spanning-tree
To permit IP broadcasts to be flooded throughout the internetwork in a controlled fashion, use the ip forward-protocol spanning-tree command in global configuration mode. To disable the flooding of IP broadcasts, use the no form of this command.
ip forward-protocol spanning-tree [any-local-broadcast]
no ip forward-protocol spanning-tree [any-local-broadcast]
Syntax Description
Defaults
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
A packet must meet the following criteria to be considered for flooding:
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A flooded UDP datagram is given the destination address specified by the ip broadcast-address command on the output interface. The destination address can be set to any desired address. Thus, the destination address may change as the datagram propagates through the network. The source address is never changed. The TTL value is decremented.
After a decision has been made to send the datagram out on an interface (and the destination address possibly changed), the datagram is handed to the normal IP output routines and is therefore subject to access lists, if they are present on the output interface.
The ip forward-protocol spanning-tree command uses the database created by the bridging Spanning-Tree Protocol. Therefore, the transparent bridging option must be in the routing software, and bridging must be configured on each interface that is to participate in the flooding in order to support this capability.
If an interface does not have bridging configured, it still will be able to receive broadcasts, but it will never forward broadcasts received on that interface. Also, it will never use that interface to send broadcasts received on a different interface.
If no actual bridging is desired, you can configure a type-code bridging filter that will deny all packet types from being bridged. Refer to the Cisco IOS Bridging and IBM Networking Configuration Guide for more information about using access lists to filter bridged traffic. The spanning-tree database is still available to the IP forwarding code to use for the flooding.
The spanning-tree-based flooding mechanism forwards packets whose contents are all ones (255.255.255.255), all zeros (0.0.0.0), and, if subnetting is enabled, all networks (10.108.255.255 as an example in the network number 10.108.0.0). This mechanism also forward packets whose contents are the zeros version of the all-networks broadcast when subnetting is enabled (for example, 10.108.0.0).
This command is an extension of the ip helper-address command, in that the same packets that may be subject to the helper address and forwarded to a single network can now be flooded. Only one copy of the packet will be put on each network segment.
Examples
The following example permits IP broadcasts to be flooded through the internetwork in a controlled fashion:
ip forward-protocol spanning-treeRelated Commands
ip forward-protocol turbo-flood
To speed up flooding of User Datagram Protocol (UDP) datagrams using the spanning-tree algorithm, use the ip forward-protocol turbo-flood command in global configuration mode. To disable this feature, use the no form of this command.
ip forward-protocol turbo-flood [udp-checksum]
no ip forward-protocol turbo-flood [udp-checksum]
Syntax Description
Command Default
Disabled
Command Modes
Global configuration
Command History
Usage Guidelines
Used in conjunction with the ip forward-protocol spanning-tree command, this command is supported over Advanced Research Projects Agency (ARPA)-encapsulated Ethernets, FDDI, and High-Level Data Link Control (HDLC) encapsulated serials, but is not supported on Token Rings. As long as the Token Rings and the non-HDLC serials are not part of the bridge group being used for UDP flooding, turbo flooding will behave normally.
When you enter the ip forward-protocol turbo-flood command, the outgoing UDP packets have a NULL checksum. If you want to have UDP checksums on all outgoing packets, you must enter the ip forward-protocol turbo-flood udp-checksum command.
Examples
The following is an example of a two-port router using this command:
ip forward-protocol turbo-floodip forward-protocol spanning-tree!interface ethernet 0ip address 10.9.1.1bridge-group 1!interface ethernet 1ip address 10.9.1.2bridge-group 1!bridge 1 protocol decThe following example shows how to speed up the flooding of UDP packets using the spanning-tree algorithm and include the UDP checksums on all outgoing packets:
ip forward-protocol turbo-flood udp-checksumRelated Commands
ip helper-address
To enable the forwarding of User Datagram Protocol (UDP) broadcasts, including BOOTP, received on an interface, use the ip helper-address command in interface configuration mode. To disable the forwarding of broadcast packets to specific addresses, use the no form of this command.
ip helper-address [vrf name | global] address [redundancy vrg-name]
no ip helper-address [vrf name | global] address [redundancy vrg-name]
Syntax Description
Defaults
Disabled.
Command Modes
Interface configuration
Command History
Usage Guidelines
Combined with the ip forward-protocol command, the ip helper-address command allows you to control which broadcast packets and which protocols are forwarded.
One common application that requires helper addresses is Dynamic Host Configuration Protocol (DHCP), which is defined in RFC 1531. To enable BOOTP or DHCP broadcast forwarding for a set of clients, configure a helper address on the router interface connected to the client. The helper address should specify the address of the BOOTP or DHCP server. If you have multiple servers, you can configure one helper address for each server.
All of the following conditions must be met in order for a UDP or IP packet to be helpered by the ip helper-address command:
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If the DHCP server resides in a Virtual Private Network (VPN) or global space that is different from the interface VPN, then the vrf name or global option allows you to specify the name of the VRF or global space in which the DHCP server resides.
The ip helper-address vrf name address option uses the address associated with the VRF name regardless of the VRF of the incoming interface. If the ip helper-address vrf name address command is configured and later the vrf is deleted from the configuration, then all IP helper addresses associated with that VRF name will be removed from the interface configuration.
If the ip helper-address address command is already configured on an interface with no VRF name configured, and later the interface is configured with the ip helper-address vrf name address command, then the previously configured ip helper-address address is considered to be global.
Note
Examples
The following example defines an address that acts as a helper address:
interface ethernet 1ip helper-address 10.24.43.2The following example defines an address that acts as a helper address and is associated with the VRF named host1:
interface ethernet 1/0ip helper-address vrf host1 10.25.44.2The following example defines an address that acts as a helper address and is associated with the VRG named group1:
interface ethernet 1/0ip helper-address 10.25.45.2 redundancy group1Related Commands
ip forward-protocol
Specifies which protocols and ports the router forwards when forwarding broadcast packets.
ip host
To define static hostname-to-address mappings in the Domain Name System (DNS) hostname cache for a DNS view, use the ip host command in global configuration mode. If the hostname cache does not exist yet, it is automatically created. To remove a hostname-to-address mapping, use the no form of this command.
ip host [vrf vrf-name] [view view-name] {hostname | tmodem-telephone-number} [tcp-port-number] {ip-address1 [ip-address2...ip-address8] | additional ip-address9 [ip-address10...ip-addressn] | [mx preference mx-server-hostname | ns nameserver-hostname | srv priority weight port target]}
no ip host [vrf vrf-name] [view view-name] {hostname | tmodem-telephone-number} [tcp-port-number] {ip-address1 [ip-address2...ip-address8] additional ip-address9 [ip-address10...ip-addressn] | [mx preference mx-server-hostname | ns nameserver-hostname | srv priority weight port target]}
Syntax Description
Command Default
No static hostname-to-address mapping is added to the DNS hostname cache for a DNS view.
Command Modes
Global configuration
Command History
Usage Guidelines
This command adds the specified hostname-to-IP address mappings as follows:
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If the specified VRF does not exist yet, a warning is displayed and the entry is added to the hostname cache anyway.
If the specified view does not exist yet, a warning is displayed and the entry is added to the hostname cache anyway.
If the hostname cache does not exist yet, it is automatically created.
To specify the machine that provides domain service for the domain, use the ns keyword and the nameserver-hostname argument
To specify where the mail for the host is to be sent, use the mx keyword and the preference and mx-server-hostname arguments.
To specify a host that offers a service in the domain, use the srv keyword and the priority, weight, port, and target arguments.
To display the display the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views, use the show hosts command.
Note
Examples
The following example shows how to add three mapping entries to the global hostname cache and then remove one of those entries from the global hostname cache:
Router(config)# ip host www.example1.com 192.168.2.141 192.168.2.241Router(config)# ip host www.example2.com 192.168.2.242Router(config)# no ip host www.example1.com 192.168.2.141The following example shows how to add three mapping entries to the hostname cache for the DNS view user3 that is associated with the VRF vpn101 and then remove one of those entries from that hostname cache:
Router(config)# ip host vrf vpn101 view user3 www.example1.com 192.168.2.141 192.168.2.241Router(config)# ip host vrf vpn101 view user3 www.example2.com 192.168.2.242Router(config)# no ip host vrf vpn101 view user3 www.example1.com 192.168.2.141Related Commands
ip hp-host
To enter into the host table the host name of a Hewlett-Packard (HP) host to be used for HP Probe Proxy service, use the ip hp-host global configuration command. To remove a host name, use the no form of this command.
ip hp-host host-name ip-address
no ip hp-host host-name ip-address
Syntax Description
Defaults
No host names are defined.
Command Modes
Global configuration
Command History
Usage Guidelines
To use the HP Probe Proxy service, you must first enter the host name of the HP host into the host table using this command.
Examples
The following example specifies the name and address of an HP host, and then enables HP Probe Proxy:
ip hp-host BCWjo 131.108.1.27interface ethernet 0ip probe proxyRelated Commands
ip probe proxy
Enables the HP Probe Proxy support, which allows the Cisco IOS software to respond to HP Probe Proxy name requests.
ip mobile arp
To enable local-area mobility, use the ip mobile arp command in interface configuration mode. To disable local-area mobility, use the no form of this command.
ip mobile arp [timers keepalive hold-time] [access-group access-list-number | name]
no ip mobile arp [timers keepalive hold-time] [access-group access-list-number | name]
Syntax Description
Defaults
Local-area mobility is disabled.
If you enable local-area mobility:
keepalive: 5 minutes (300 seconds)
hold-time: 15 minutes (900 seconds)Command Modes
Interface configuration
Command History
Usage Guidelines
Local-area mobility is supported on Ethernet, Token Ring, and FDDI interfaces only.
To create larger mobility areas, you must first redistribute the mobile routes into your Interior Gateway Protocol (IGP). The IGP must support host routes. You can use Enhanced IGRP, Open Shortest Path First (OSPF), or Intermediate System-to-Intermediate System (IS-IS); you can also use Routing Information Protocol (RIP), but RIP is not recommended. The mobile area must consist of a contiguous set of subnets.
Using an access list to control the list of possible mobile nodes is strongly encouraged. Without an access list, misconfigured hosts can be taken for mobile nodes and disrupt normal operations.
Examples
The following example configures local-area mobility on Ethernet interface 0:
access-list 10 permit 10.92.37.114interface ethernet 0ip mobile arp access-group 10Related Commands
ip netmask-format
To specify the format in which netmasks are displayed in show command output, use the ip netmask-format command in line configuration mode. To restore the default display format, use the no form of this command.
ip netmask-format {bit-count | decimal | hexadecimal}
no ip netmask-format {bit-count | decimal | hexadecimal}
Syntax Description
Defaults
Netmasks are displayed in dotted-decimal format.
Command Modes
Line configuration
Command History
Usage Guidelines
IP uses a 32-bit mask that indicates which address bits belong to the network and subnetwork fields, and which bits belong to the host field. This is called a netmask. By default, show commands display an IP address and then its netmask in dotted decimal notation. For example, a subnet would be displayed as 10.108.11.0 255.255.255.0.
However, you can specify that the display of the network mask appear in hexadecimal format or bit count format instead. The hexadecimal format is commonly used on UNIX systems. The previous example would be displayed as 10.108.11.0 0XFFFFFF00.
The bitcount format for displaying network masks is to append a slash (/) and the total number of bits in the netmask to the address itself. The previous example would be displayed as 10.108.11.0/24.
Examples
The following example configures network masks for the specified line to be displayed in bitcount notation in the output of show commands:
line vty 0 4ip netmask-format bitcountip probe proxy
To enable the HP Probe Proxy support, which allows the Cisco IOS software to respond to HP Probe Proxy name requests, use the ip probe proxy interface configuration command. To disable HP Probe Proxy, use the no form of this command.
ip probe proxy
no ip probe proxy
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Interface configuration
Command History
Usage Guidelines
HP Probe Proxy Name requests are typically used at sites that have Hewlett-Packard (HP) equipment and are already using HP Probe.
To use the HP Probe Proxy service, you must first enter the host name of the HP host into the host table using the ip hp-host global configuration command.
Examples
The following example specifies an HP host name and address, and then enables Probe Proxy:
ip hp-host BCWjo 131.108.1.27interface ethernet 0ip probe proxyRelated Commands
ip hp-host
Enters into the host table the host name of an HP host to be used for HP Probe Proxy service.
ip route
To establish static routes, use the ip route command in global configuration mode. To remove static routes, use the no form of this command.
ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [dhcp] [distance] [name next-hop-name] [permanent | track number] [tag tag]
no ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [dhcp] [distance] [name next-hop-name] [permanent | track number] [tag tag]
Syntax Description
Defaults
No static routes are established.
Command Modes
Global configuration (config)
Command History
Usage Guidelines
The establishment of a static route is appropriate when the Cisco IOS software cannot dynamically build a route to the destination.
When you specify a DHCP server to assign a static route, the interface type and number and administrative distance may be configured also.
If you specify an administrative distance, you are flagging a static route that can be overridden by dynamic information. For example, routes derived with Enhanced Interior Gateway Routing Protocol (EIGRP) have a default administrative distance of 100. To have a static route that would be overridden by an EIGRP dynamic route, specify an administrative distance greater than 100. Static routes have a default administrative distance of 1.
Static routes that point to an interface on a connected router will be advertised by way of Routing Information Protocol (RIP) and EIGRP regardless of whether redistribute static commands are specified for those routing protocols. This situation occurs because static routes that point to an interface are considered in the routing table to be connected and hence lose their static nature. Also, the target of the static route should be included in the network (DHCP) command. If this condition is not met, no dynamic routing protocol will advertise the route unless a redistribute static command is specified for these protocols. With the following configuration:
rtr1 (serial 172.16.188.1/30)--------------> rtr2(Fast Ethernet 172.31.1.1/30) ------>router [rip | eigrp]network 172.16.188.0network 172.31.0.0•
ip route 172.16.188.252 255.255.255.252 FastEthernet 0/0RIP and EIGRP do not redistribute the route with the following ip route command because of the split horizon algorithm:
ip route 172.16.188.252 255.255.255.252 serial 2/1•
ip route 172.16.188.252 255.255.255.252 FastEthernet 0/0ip route 172.16.188.252 255.255.255.252 serial 2/1With the Open Shortest Path First (OSPF) protocol, static routes that point to an interface are not advertised unless a redistribute static command is specified.
Adding a static route to an Ethernet or other broadcast interface (for example, ip route 0.0.0.0 0.0.0.0 Ethernet 1/2) will cause the route to be inserted into the routing table only when the interface is up. This configuration is not generally recommended. When the next hop of a static route points to an interface, the router considers each of the hosts within the range of the route to be directly connected through that interface, and therefore it will send Address Resolution Protocol (ARP) requests to any destination addresses that route through the static route.
The practical implication of configuring the ip route 0.0.0.0 0.0.0.0 ethernet 1/2 command is that the router will consider all of the destinations that the router does not know how to reach through some other route as directly connected to Ethernet interface 1/2. So the router will send an ARP request for each host for which it receives packets on this network segment. This configuration can cause high processor utilization and a large ARP cache (along with memory allocation failures). Configuring a default route or other static route that directs the router to forward packets for a large range of destinations to a connected broadcast network segment can cause your router to reload.
Specifying a numerical next hop that is on a directly connected interface will prevent the router from using proxy ARP. However, if the interface with the next hop goes down and the numerical next hop can be reached through a recursive route, you may specify both the next hop and interface (for example, ip route 0.0.0.0 0.0.0.0 ethernet 1/2 10.1.2.3) with a static route to prevent routes from passing through an unintended interface.
The name next-hop-name keyword and argument combination allows you to associate static routes with names in your running configuration. If you have several static routes, you can specify names that describe the purpose of each static route in order to more easily identify each one.
The track number keyword and argument combination specifies that the static route will be installed only if the state of the configured track object is up.
Examples
The following example chooses an administrative distance of 110. In this case, packets for network 10.0.0.0 will be routed to a router at 172.31.3.4 if dynamic information with an administrative distance less than 110 is not available.
ip route 10.0.0.0 255.0.0.0 172.31.3.4 110
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The following example routes packets for network 172.31.0.0 to a router at 172.31.6.6:
ip route 172.31.0.0 255.255.0.0 172.31.6.6The following example routes packets for network 192.168.1.0 directly to the next hop at 10.1.2.3. If the interface goes down, this route is removed from the routing table and will not be restored unless the interface comes back up.
ip route 192.168.1.0 255.255.0.0 Ethernet 0 10.1.2.3The following example installs the static route only if the state of track object 123 is up:
ip route 0.0.0.0 0.0.0.0 Ethernet 0/1 10.1.1.242 track 123The following example shows that using the dhcp keyword in a configuration of Ethernet interfaces 1 and 2 enables the interfaces to obtain the next-hop router IP addresses dynamically from a DHCP server:
ip route 10.165.200.225 255.255.255.255 ether1 dhcpip route 10.165.200.226 255.255.255.255 ether2 dhcp 20The following example shows that using the name next-hop-name keyword and argument combination for each static route in the configuration helps you remember the purpose for each static route.
ip route 172.0.0.0 255.0.0.0 10.0.0.1 name Seattle2DetroitThe name for the static route will be displayed when the show running-configuration command is entered:
Router# show running-config | include ip routeip route 172.0.0.0 255.0.0.0 10.0.0.1 name Seattle2DetroitRelated Commands
ip routing
To enable IP routing, use the ip routing command in global configuration mode. To disable IP routing, use the no form of this command.
ip routing
no ip routing
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Usage Guidelines
To bridge IP, the no ip routing command must be configured to disable IP routing. However, you need not specify no ip routing in conjunction with concurrent routing and bridging to bridge IP.
The ip routing command is disabled on the Cisco VG200 voice over IP gateway.
Examples
The following example enables IP routing:
ip routingip source binding
To add a static IP source binding entry, use the ip source binding command. Use the no form of this command to delete a static IP source binding entry
ip source binding mac-address vlan vlan-id ip-address interface type mod/port
[no] ip source binding mac-address vlan vlan-id ip-address interface type mod/port
Syntax Description
Command Default
No IP source bindings are configured.
Command Modes
Global configuration (config)
Command History
Usage Guidelines
You can use this command to add a static IP source binding entry only.
The no format deletes the corresponding IP source binding entry. It requires the exact match of all required parameter in order for the deletion to be successful. Note that each static IP binding entry is keyed by a MAC address and a VLAN number. If the command contains the existing MAC address and VLAN number, the existing binding entry is updated with the new parameters instead of creating a separate binding entry.
Examples
This example shows how to add a static IP source binding entry:
Router(config)#ip source binding 000C.0203.0405 vlan 100 172.16.30.2 interface gigabitethernet5/3This example shows how to delete a static IP source binding entry:
Router(config)#no ip source binding 000C.0203.0405 vlan 100 172.16.30.2 interface gigabitethernet5/3Related Commands
ip source-route
To allow the Cisco IOS software to handle IP datagrams with source routing header options, use the ip source-route command in global configuration mode. To have the software discard any IP datagram containing a source-route option, use the no form of this command.
ip source-route
no ip source-route
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Examples
The following example enables the handling of IP datagrams with source routing header options:
ip source-routeRelated Commands
ip subnet-zero
To enable the use of subnet 0 for interface addresses and routing updates, use the ip subnet-zero command in global configuration mode. To restore the default, use the no form of this command.
ip subnet-zero
no ip subnet-zero
Syntax Description
This command has no arguments or keywords.
Defaults
Enabled
Command Modes
Global configuration
Command History
Usage Guidelines
The ip subnet-zero command provides the ability to configure and route to subnet 0 subnets.
Subnetting with a subnet address of 0 is discouraged because of the confusion inherent in having a network and a subnet with indistinguishable addresses.
Examples
The following example enables subnet zero:
ip subnet-zeroip unnumbered
To enable IP processing on an interface without assigning an explicit IP address to the interface, use the ip unnumbered command in interface configuration mode or subinterface configuration mode. To disable the IP processing on the interface, use the no form of this command.
ip unnumbered type number
no ip unnumbered type number
Syntax Description
Command Default
IP processing on the unnumbered interface is disabled.
Command Modes
Interface configuration
Subinterface configurationCommand History
Usage Guidelines
When an unnumbered interface generates a packet (for example, for a routing update), it uses the address of the specified interface as the source address of the IP packet. It also uses the address of the specified interface in determining which routing processes are sending updates over the unnumbered interface. Restrictions are as follows:
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•
•
•
•
The interface you specify by the type and `number arguments must be enabled (listed as "up" in the show interfaces command display).
If you are configuring Intermediate System-to-Intermediate System (IS-IS) across a serial line, you should configure the serial interfaces as unnumbered. This configuration allows you to comply with RFC 1195, which states that IP addresses are not required on each interface.
Note
Examples
In the following example, the first serial interface is given the address of Ethernet 0:
interface ethernet 0ip address 10.108.6.6 255.255.255.0!interface serial 0ip unnumbered ethernet 0In the following example, Ethernet VLAN subinterface 3/0.2 is configured as an IP unnumbered subinterface:
interface ethernet 3/0.2encapsulation dot1q 200ip unnumbered ethernet 3/1In the following example, Fast Ethernet subinterfaces in the range from 5/1.1 to 5/1.4 are configured as IP unnumbered subinterfaces:
interface range fastethernet5/1.1 - fastethernet5/1.4ip unnumbered ethernet 3/1ip verify source vlan dhcp-snooping
To enable per l2-port IP source guard, use the ip verify source vlan dhcp-snooping command. Use the no form of this command to disable per l2-port IP source guard.
ip verify source vlan dhcp-snooping
no ip verify source vlan dhcp-snooping
Syntax Description
This command has no arguments or keywords.
Command Default
Per 12-port IP source guard is disabled.
Command Modes
Interface configuration (config-if)
Command History
Usage Guidelines
The ip verify source vlan dhcp-snooping command enables all the VLANs on the interface that have DHCP snooping enabled.
Examples
This example shows how to enable per l2-port IP source guard on an interface:
Router(config-if)#ip verify source vlan dhcp-snoopingThis example shows how to disable per l2-port IP source guard on an interface:
Router(config-if)#no ip verify source vlan dhcp-snoopingRelated Commands
show hosts
To display the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular Domain Name System (DNS) view or for all configured DNS views, use the show hosts command in privileged EXEC mode.
show hosts [vrf vrf-name] [view view-name] [all | hostname] [summary]
Syntax Description
Command Modes
Privileged EXEC
Command History
Usage Guidelines
This command displays the default domain name, the style of name lookup service, a list of name server hosts, and the cached list of hostnames and addresses specific to a particular DNS view or for all configured DNS views.
If you specify the show hosts command without any optional keywords or arguments, only the entries in the global hostname cache will be displayed.
If the output from this command extends beyond the bottom of the screen, press the Space bar to continue or press the Q-key to terminate command output.
Examples
The following is sample output from the show hosts command with no parameters specified:
Router# show hostsDefault domain is CISCO.COMName/address lookup uses domain serviceName servers are 192.0.2.220Host Flag Age Type Address(es)EXAMPLE1.CISCO.COM (temp, OK) 1 IP 192.0.2.10EXAMPLE2.CISCO.COM (temp, OK) 8 IP 192.0.2.50EXAMPLE3.CISCO.COM (temp, OK) 8 IP 192.0.2.115EXAMPLE4.CISCO.COM (temp, EX) 8 IP 192.0.2.111EXAMPLE5.CISCO.COM (temp, EX) 0 IP 192.0.2.27EXAMPLE6.CISCO.COM (temp, EX) 24 IP 192.0.2.30The following is sample output from the show hosts command that specifies the VRF vpn101:
Router# show hosts vrf vpn101Default domain is example.comDomain list: example1.com, example2.com, example3.comName/address lookup uses domain serviceName servers are 192.0.2.204, 192.0.2.205, 192.0.2.206Codes: UN - unknown, EX - expired, OK - OK, ?? - revalidatetemp - temporary, perm - permanentNA - Not Applicable None - Not definedHost Port Flags Age Type Address(es)user None (perm, OK) 0 IP 192.0.2.001www.example.com None (perm, OK) 0 IP 192.0.2.111192.0.2.112Table 11 describes the significant fields shown in the display.
Related Commands
show ip aliases
To display the IP addresses mapped to TCP ports (aliases) and Serial Line Internet Protocol (SLIP) addresses, which are treated similarly to aliases, use the show ip aliases EXEC command.
show ip aliases
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Usage Guidelines
To distinguish a SLIP address from a normal alias address, the command output uses the form SLIP TTY1 for the "port" number, where 1 is the auxiliary port.
Examples
The following is sample output from the show ip aliases command:
Router# show ip aliasesIP Address Port10.108.29.245 SLIP TTY1The display lists the IP address and corresponding port number.
Related Commands
show ip interface
To display the usability status of interfaces configured for IP, use the show ip interface command in privileged EXEC mode.
show ip interface [type number] [brief]
Syntax Description
type
(Optional) Interface type.
number
(Optional) Interface number.
brief
(Optional) Displays a summary of the usability status information for each interface.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
The Cisco IOS software automatically enters a directly connected route in the routing table if the interface is usable. A usable interface can send and receive packets. If an interface is not usable, the directly connected routing entry is removed from the routing table. Removing the entry allows the software to use dynamic routing protocols to determine backup routes to the network, if any.
If the interface can provide two-way communication, the line protocol is marked "up." If the interface hardware is usable, the interface is marked "up."
If you specify an optional interface type, you see information for that specific interface.
If you specify no optional arguments, you see information on all the interfaces.
When an asynchronous interface is encapsulated with PPP or Serial Line Internet Protocol (SLIP), IP fast switching is enabled. A show ip interface command on an asynchronous interface encapsulated with PPP or SLIP displays a message indicating that IP fast switching is enabled.
The show ip interface brief command can be used to view a summary of the router interfaces. This command displays the IP address, interface status, and additional information.
The show ip interface brief command does not display any information related to URPF.
Examples
The following examples from Cisco IOS Release 12.3(14)YM2 show:
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The highlighted arrows (for documentation purposes only) show the configured output and input features and the additional MPF interface information.
Router# show running-config interface gigabitethernet 0/3interface GigabitEthernet0/3ip address 10.1.1.1 255.255.0.0ip flow egress <== outputip policy route-map PBR_NAME <== inputduplex autospeed automedia-type gbicnegotiation autoendRouter# show ip interface gigabitethernet 0/3GigabitEthernet0/3 is up, line protocol is upInternet address is 10.1.1.1/16Broadcast address is 255.255.255.255Address determined by setup commandMTU is 1500 bytesHelper address is not setDirected broadcast forwarding is disabledOutgoing access list is not setInbound access list is not setProxy ARP is enabledLocal Proxy ARP is disabledSecurity level is defaultSplit horizon is enabledICMP redirects are always sentICMP unreachables are always sentICMP mask replies are never sentIP fast switching is enabledIP fast switching on the same interface is disabledIP Flow switching is disabledIP CEF switching is enabledIP Feature Fast switching turbo vectorIP VPN Flow CEF switching turbo vectorIP multicast fast switching is enabledIP multicast distributed fast switching is disabledIP route-cache flags are Fast, CEFRouter Discovery is disabledIP output packet accounting is disabledIP access violation accounting is disabledTCP/IP header compression is disabledRTP/IP header compression is disabledPolicy routing is enabled, using route map PBRNetwork address translation is disabledBGP Policy Mapping is disabledIP Multi-Processor Forwarding is enabled <======== MPF informationIP Input features, "PBR",are not supported by MPF and are IGNOREDIP Output features, "NetFlow",are not supported by MPF and are IGNOREDThe following example identifies a downstream VRF. The highlighted line (for documentation purposes only) identifies the downstream VRF.
Router# show ip interface vi 3Virtual-Access3 is up, line protocol is upInterface is unnumbered. Using address of Loopback2 (10.0.0.8)Broadcast address is 255.255.255.255Peer address is 10.8.1.1MTU is 1492 bytesHelper address is not setDirected broadcast forwarding is disabledOutgoing access list is not setInbound access list is not setProxy ARP is enabledLocal Proxy ARP is disabledSecurity level is defaultSplit horizon is enabledICMP redirects are always sentICMP unreachables are always sentICMP mask replies are never sentIP fast switching is enabledIP fast switching on the same interface is enabledIP Flow switching is disabledIP CEF switching is enabledIP Feature Fast switching turbo vectorIP VPN CEF switching turbo vectorVPN Routing/Forwarding "U"Downstream VPN Routing/Forwarding "D"IP multicast fast switching is disabledIP multicast distributed fast switching is disabledIP route-cache flags are Fast, CEFRouter Discovery is disabledIP output packet accounting is disabledIP access violation accounting is disabledTCP/IP header compression is disabledRTP/IP header compression is disabledPolicy routing is disabledNetwork address translation is disabledWCCP Redirect outbound is disabledWCCP Redirect inbound is disabledWCCP Redirect exclude is disabledBGP Policy Mapping is disabledThe following example shows the information displayed when URPF drop-rate notification is configured:
Router# show ip interface ethernet 2/3Ethernet2/3 is up, line protocol is upInternet address is 10.0.0.4/16Broadcast address is 255.255.255.255Address determined by non-volatile memoryMTU is 1500 bytesHelper address is not setDirected broadcast forwarding is disabledOutgoing access list is not setInbound access list is not setProxy ARP is enabledLocal Proxy ARP is disabledSecurity level is defaultSplit horizon is enabledICMP redirects are always sentICMP unreachables are always sentICMP mask replies are never sentIP fast switching is disabledIP Flow switching is disabledIP CEF switching is disabledIP Null turbo vectorIP Null turbo vectorIP multicast fast switching is disabledIP multicast distributed fast switching is disabledIP route-cache flags are No CEFRouter Discovery is disabledIP output packet accounting is disabledIP access violation accounting is disabledTCP/IP header compression is disabledRTP/IP header compression is disabledProbe proxy name replies are disabledPolicy routing is disabledNetwork address translation is disabledWCCP Redirect outbound is disabledWCCP Redirect inbound is disabledWCCP Redirect exclude is disabledBGP Policy Mapping is disabledURPF Information
Input features: uRPFIP verify source reachable-via RX, allow default0 verification drops0 suppressed verification drops0 verification drop-raterouter#This example shows how to display the usability status for a specific VLAN:
Router# show ip interface vlan 1Vlan1 is up, line protocol is upInternet address is 10.0.0.4/24Broadcast address is 255.255.255.255Address determined by non-volatile memoryMTU is 1500 bytesHelper address is not setDirected broadcast forwarding is disabledOutgoing access list is not setInbound access list is not setProxy ARP is enabledLocal Proxy ARP is disabledSecurity level is defaultSplit horizon is enabledICMP redirects are always sentICMP unreachables are always sentICMP mask replies are never sentIP fast switching is enabledIP fast switching on the same interface is disabledIP Flow switching is disabledIP CEF switching is enabledIP Fast switching turbo vectorIP Normal CEF switching turbo vectorIP multicast fast switching is enabledIP multicast distributed fast switching is disabledIP route-cache flags are Fast, CEFRouter Discovery is disabledIP output packet accounting is disabledIP access violation accounting is disabledTCP/IP header compression is disabledRTP/IP header compression is disabledProbe proxy name replies are disabledPolicy routing is disabledNetwork address translation is disabledWCCP Redirect outbound is disabledWCCP Redirect inbound is disabledWCCP Redirect exclude is disabledBGP Policy Mapping is disabledSampled Netflow is disabledIP multicast multilayer switching is disabledNetflow Data Export (hardware) is enabledTable 12 describes the significant fields shown in the display.
The following is sample output from the show ip interface brief command:
Router# show ip interface briefInterface IP-Address OK? Method Status ProtocolEthernet0 10.108.00.5 YES NVRAM up upEthernet1 unassigned YES unset administratively down downLoopback0 10.108.200.5 YES NVRAM up upSerial0 10.108.100.5 YES NVRAM up upSerial1 10.108.40.5 YES NVRAM up upSerial2 10.108.100.5 YES manual up upSerial3 unassigned YES unset administratively down downTable 13 describes the significant fields shown in the display.
Related Commands
show ip irdp
To display ICMP Router Discovery Protocol (HRDP) values, use the show ip irdp command in EXEC mode.
show ip irdp
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
Examples
The following is sample output from the show ip irdp command:
Router# show ip irdpEthernet 0 has router discovery enabledAdvertisements will occur between every 450 and 600 seconds.Advertisements are valid for 1800 seconds.Default preference will be 100.--More--Serial 0 has router discovery disabled--More--Ethernet 1 has router discovery disabledAs the display shows, show ip irdp output indicates whether router discovery has been configured for each router interface, and it lists the values of router discovery configurables for those interfaces on which router discovery has been enabled. Explanations for the less obvious lines of output in the display are as follows:
Advertisements will occur between every 450 and 600 seconds.This indicates the configured minimum and maximum advertising interval for the interface.
Advertisements are valid for 1800 seconds.This indicates the configured holdtime values for the interface.
Default preference will be 100.This indicates the configured (or in this case default) preference value for the interface.
Related Commands
show ip masks
To display the masks used for network addresses and the number of subnets using each mask, use the show ip masks command in EXEC mode.
show ip masks address
Syntax Description
Command Modes
EXEC
Command History
Usage Guidelines
The show ip masks command is useful for debugging when a variable-length subnet mask (VLSM) is used. It shows the number of masks associated with the network and the number of routes for each mask.
Examples
The following is sample output from the show ip masks command:
Router# show ip masks 172.16.0.0Mask Reference count255.255.255.255 2255.255.255.0 3255.255.0.0 1show ip route
To display the current state of the routing table, use the show ip route command in user EXEC or privileged EXEC mode.
show ip route [ip-address [mask] [longer-prefixes] | protocol [process-id] | list [access-list-number | access-list-name] | static download]
Syntax Description
Command Modes
User EXEC
Privileged EXECCommand History
Usage Guidelines
The show ip route static download command provides a way to display all dynamic static routes with name and distance information, including active and inactive ones. You can display all active dynamic static routes with both the show ip route and show ip route static commands after these active routes are added in the main routing table.
Examples
Routing Table Examples
The following examples show the standard routing tables displayed by the show ip route command. Use the codes displayed at the beginning of each report and the information in Table 14 to understand the type of route.
The following is sample output from the show ip route command when entered without an address:
Router# show ip routeCodes: R - RIP derived, O - OSPF derived,C - connected, S - static, B - BGP derived,* - candidate default route, IA - OSPF inter area route,i - IS-IS derived, ia - IS-IS, U - per-user static route,o - on-demand routing, M - mobile, P - periodic downloaded static route,D - EIGRP, EX - EIGRP external, E1 - OSPF external type 1 route,E2 - OSPF external type 2 route, N1 - OSPF NSSA external type 1 route,N2 - OSPF NSSA external type 2 routeGateway of last resort is 10.119.254.240 to network 10.140.0.0O E2 10.110.0.0 [160/5] via 10.119.254.6, 0:01:00, Ethernet2E 10.67.10.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2O E2 10.68.132.0 [160/5] via 10.119.254.6, 0:00:59, Ethernet2O E2 10.130.0.0 [160/5] via 10.119.254.6, 0:00:59, Ethernet2E 10.128.0.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2E 10.129.0.0 [200/129] via 10.119.254.240, 0:02:22, Ethernet2E 10.65.129.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2E 10.10.0.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2E 10.75.139.0 [200/129] via 10.119.254.240, 0:02:23, Ethernet2E 10.16.208.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2E 10.84.148.0 [200/129] via 10.119.254.240, 0:02:23, Ethernet2E 10.31.223.0 [200/128] via 10.119.254.244, 0:02:22, Ethernet2E 10.44.236.0 [200/129] via 10.119.254.240, 0:02:23, Ethernet2E 10.141.0.0 [200/129] via 10.119.254.240, 0:02:22, Ethernet2E 10.140.0.0 [200/129] via 10.119.254.240, 0:02:23, Ethernet2The following is sample output that includes IS-IS Level 2 routes learned:
Router# show ip routeCodes: R - RIP derived, O - OSPF derived,C - connected, S - static, B - BGP derived,* - candidate default route, IA - OSPF inter area route,i - IS-IS derived, ia - IS-IS, U - per-user static route,o - on-demand routing, M - mobile, P - periodic downloaded static route,D - EIGRP, EX - EIGRP external, E1 - OSPF external type 1 route,E2 - OSPF external type 2 route, N1 - OSPF NSSA external type 1 route,N2 - OSPF NSSA external type 2 routeGateway of last resort is not set10.89.0.0 is subnetted (mask is 255.255.255.0), 3 subnetsC 10.89.64.0 255.255.255.0 is possibly down,routing via 0.0.0.0, Ethernet0i L2 10.89.67.0 [115/20] via 10.89.64.240, 0:00:12, Ethernet0i L2 10.89.66.0 [115/20] via 10.89.64.240, 0:00:12, Ethernet0The following is sample output using the longer-prefixes keyword. When the longer-prefixes keyword is included, the address and mask pair becomes the prefix, and any address that matches that prefix is displayed. Therefore, multiple addresses are displayed.
In the following example, the logical AND operation is performed on the source address 10.0.0.0 and the mask 10.0.0.0, resulting in 10.0.0.0. Each destination in the routing table is also logically ANDed with the mask and compared to that result of 10.0.0.0. Any destinations that fall into that range are displayed in the output.
Router# show ip route 10.0.0.0 10.0.0.0 longer-prefixesCodes: R - RIP derived, O - OSPF derived,C - connected, S - static, B - BGP derived,* - candidate default route, IA - OSPF inter area route,i - IS-IS derived, ia - IS-IS, U - per-user static route,o - on-demand routing, M - mobile, P - periodic downloaded static route,D - EIGRP, EX - EIGRP external, E1 - OSPF external type 1 route,E2 - OSPF external type 2 route, N1 - OSPF NSSA external type 1 route,N2 - OSPF NSSA external type 2 routeGateway of last resort is not setS 10.134.0.0 is directly connected, Ethernet0S 10.10.0.0 is directly connected, Ethernet0S 10.129.0.0 is directly connected, Ethernet0S 10.128.0.0 is directly connected, Ethernet0S 10.49.246.0 is directly connected, Ethernet0S 10.160.97.0 is directly connected, Ethernet0S 10.153.88.0 is directly connected, Ethernet0S 10.76.141.0 is directly connected, Ethernet0S 10.75.138.0 is directly connected, Ethernet0S 10.44.237.0 is directly connected, Ethernet0S 10.31.222.0 is directly connected, Ethernet0S 10.16.209.0 is directly connected, Ethernet0S 10.145.0.0 is directly connected, Ethernet0S 10.141.0.0 is directly connected, Ethernet0S 10.138.0.0 is directly connected, Ethernet0S 10.128.0.0 is directly connected, Ethernet010.19.0.0 255.255.255.0 is subnetted, 1 subnetsC 10.19.64.0 is directly connected, Ethernet010.69.0.0 is variably subnetted, 2 subnets, 2 masksC 10.69.232.32 255.255.255.240 is directly connected, Ethernet0S 10.69.0.0 255.255.0.0 is directly connected, Ethernet0The following examples display all downloaded static routes. A P designates which route was installed using AAA route download.
Router# show ip routeCodes: C - connected, S - static, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter areaN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate defaultU - per-user static route, o - ODR, P - periodic downloaded static routeT - traffic engineered routeGateway of last resort is 172.21.17.1 to network 0.0.0.0172.31.0.0/32 is subnetted, 1 subnetsP 172.31.229.41 is directly connected, Dialer1 20.0.0.0/24 is subnetted, 3 subnetsP 10.1.1.0 [200/0] via 172.31.229.41, Dialer1P 10.1.3.0 [200/0] via 172.31.229.41, Dialer1P 10.1.2.0 [200/0] via 172.31.229.41, Dialer1Router# show ip route static172.27.4.0/8 is variably subnetted, 2 subnets, 2 masksP 172.1.1.1/32 is directly connected, BRI0P 172.27.4.0/8 [1/0] via 103.1.1.1, BRI0S 172.31.0.0/16 [1/0] via 172.21.114.65, Ethernet0S 10.0.0.0/8 is directly connected, BRI0P 10.0.0.0/8 is directly connected, BRI0172.21.0.0/16 is variably subnetted, 5 subnets, 2 masksS 172.21.114.201/32 is directly connected, BRI0S 172.21.114.205/32 is directly connected, BRI0S 172.21.114.174/32 is directly connected, BRI0S 172.21.114.12/32 is directly connected, BRI0P 10.0.0.0/8 is directly connected, BRI0P 10.1.0.0/8 is directly connected, BRI0P 10.2.2.0/8 is directly connected, BRI0S* 0.0.0.0/0 [1/0] via 172.21.114.65, Ethernet0S 172.29.0.0/16 [1/0] via 172.21.114.65, Ethernet0The following example shows how to use the show ip route static download command to display all active and inactive routes installed using AAA route download:
Router# show ip route static downloadConnectivity: A - Active, I - InactiveA 10.10.0.0 255.0.0.0 BRI0A 10.11.0.0 255.0.0.0 BRI0A 10.12.0.0 255.0.0.0 BRI0A 10.13.0.0 255.0.0.0 BRI0I 10.20.0.0 255.0.0.0 172.21.1.1I 10.22.0.0 255.0.0.0 Serial0I 10.30.0.0 255.0.0.0 Serial0I 10.31.0.0 255.0.0.0 Serial1I 10.32.0.0 255.0.0.0 Serial1A 10.34.0.0 255.0.0.0 192.168.1.1A 10.36.1.1 255.255.255.255 BRI0 200 name remote1I 10.38.1.9 255.255.255.0 192.168.69.1
Specific Route Information
When you specify that you want information about a specific network displayed, more detailed statistics are shown. The following is sample output from the show ip route command when entered with the IP address 10.0.0.1:
Router# show ip route 10.0.0.1Routing entry for 10.0.0.1/32Known via "isis", distance 115, metric 20, type level-1Redistributing via isisLast update from 10.191.255.251 on Fddi1/0, 00:00:13 agoRouting Descriptor Blocks:* 10.22.22.2, from 10.191.255.247, via Serial2/3Route metric is 20, traffic share count is 110.191.255.251, from 10.191.255.247, via Fddi1/0Route metric is 20, traffic share count is 1When an IS-IS router advertises its link-state information, it includes one of its own IP addresses to be used as the originator IP address. When other routers calculate IP routes, they can store the originator IP address with each route in the routing table.
The example above shows the output from the show ip route command when looking at an IP route generated by IS-IS. Each path that is shown under the Routing Descriptor Blocks report displays two IP addresses. The first address (10.22.22.2) is the next hop address. The second is the originator IP address from the advertising IS-IS router. This address helps you determine where a particular IP route has originated in your network. In the example the route to 10.0.0.1/32 was originated by a router with IP address 10.191.255.247.
Table 15 describes the significant fields shown when using the show ip route command with an IP address.
The following is sample output using the longer-prefixes keyword. When the longer-prefixes keyword is included, the address and mask pair becomes the prefix, and any address that matches that prefix is displayed. Therefore, multiple addresses are displayed.
In the following example, the logical AND operation is performed on the source address 10.0.0.0 and the mask 10.0.0.0, resulting in 10.0.0.0. Each destination in the routing table is also logically ANDed with the mask and compared to that result of 10.0.0.0. Any destinations that fall into that range are displayed in the output.
Router# show ip route 10.0.0.0 10.0.0.0 longer-prefixesCodes: R - RIP derived, O - OSPF derived,C - connected, S - static, B - BGP derived,* - candidate default route, IA - OSPF inter area route,i - IS-IS derived, ia - IS-IS, U - per-user static route,o - on-demand routing, M - mobile, P - periodic downloaded static route,D - EIGRP, EX - EIGRP external, E1 - OSPF external type 1 route,E2 - OSPF external type 2 route, N1 - OSPF NSSA external type 1 route,N2 - OSPF NSSA external type 2 routeGateway of last resort is not setS 10.134.0.0 is directly connected, Ethernet0S 10.10.0.0 is directly connected, Ethernet0S 10.129.0.0 is directly connected, Ethernet0S 10.128.0.0 is directly connected, Ethernet0S 10.49.246.0 is directly connected, Ethernet0S 10.160.97.0 is directly connected, Ethernet0S 10.153.88.0 is directly connected, Ethernet0S 10.76.141.0 is directly connected, Ethernet0S 10.75.138.0 is directly connected, Ethernet0S 10.44.237.0 is directly connected, Ethernet0S 10.31.222.0 is directly connected, Ethernet0S 10.16.209.0 is directly connected, Ethernet0S 10.145.0.0 is directly connected, Ethernet0S 10.141.0.0 is directly connected, Ethernet0S 10.138.0.0 is directly connected, Ethernet0S 10.128.0.0 is directly connected, Ethernet010.19.0.0 255.255.255.0 is subnetted, 1 subnetsC 10.19.64.0 is directly connected, Ethernet010.69.0.0 is variably subnetted, 2 subnets, 2 masksC 10.69.232.32 255.255.255.240 is directly connected, Ethernet0S 10.69.0.0 255.255.0.0 is directly connected, Ethernet0The following output includes the tag 120 applied to the route 10.22.0.0/16. You must specify an IP prefix in order to see the tag value.
Router# show ip route 10.22.0.0Routing entry for 10.22.0.0/16Known via "isis", distance 115, metric 12Tag 120, type level-1Redistributing via isisLast update from 172.19.170.12 on Ethernet2, 01:29:13 agoRouting Descriptor Blocks:* 172.19.170.12, from 10.3.3.3, via Ethernet2Route metric is 12, traffic share count is 1Route tag 120Static Routes Using a DHCP Gateway Examples
The following example shows that IP route 10.8.8.0 is directly connected to the Internet and is the next-hop (option 3) default gateway. Routes 10.1.1.1 [1/0], 10.3.2.1 [24/0], and 172.2.2.2 [1/0] are static, and route 10.0.0.0/0 is a default route candidate.
Router# show ip routeCodes: C - connected, S - static, R - RIP, M - mobile, B - BGPD - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter areaN1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2ia - IS-IS inter area, * - candidate default, U - per-user static routeo - ODR, P - periodic downloaded static routeGateway of last resort is 10.0.19.14 to network 0.0.0.010.0.0.0/24 is subnetted, 1 subnetsC 10.8.8.0 is directly connected, Ethernet110.0.0.0/32 is subnetted, 1 subnetsS 10.1.1.1 [1/0] via 10.8.8.110.0.0.0/32 is subnetted, 1 subnetsS 10.3.2.1 [24/0] via 10.8.8.1172.16.0.0/32 is subnetted, 1 subnetsS 172.2.2.2 [1/0] via 10.8.8.110.0.0.0/28 is subnetted, 1 subnetsC 10.0.19.0 is directly connected, Ethernet010.0.0.0/24 is subnetted, 1 subnetsC 10.15.15.0 is directly connected, Loopback0S* 10.0.0.0/0 [1/0] via 10.0.19.14Related Commands
show ip source binding
To display IP-source bindings configured on the system, use the show ip source command command in privileged EXEC mode.
show ip source binding [ip-address] [mac-address] [dhcp-snooping | static] [vlan vlan-id] [interface type mod/port]
Syntax Description
Command Default
Both static and DHCP-snooping bindings are displayed.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Each optional parameter is used to filter the display output.
Examples
This example shows the output without entering any keywords:
Router(config)#show ip source bindingMacAddress IpAddress Lease(sec) Type VLAN Interface------------------ --------------- ---------- ------------- ---- --------------------00:00:00:0A:00:0B 17.16.0.1 infinite static 10 FastEthernet6/1000:00:00:0A:00:0A 17.16.0.2 10000 dhcp-snooping 10 FastEthernet6/11This example shows how to display the static IP binding entry for a specific IP address:
Router# show ip source binding 17.16.0.1 0000.000A.000B static vlan 10 interface gigabitethernet6/10MacAddress IpAddress Lease(sec) Type VLAN Interface------------------ --------------- ---------- ------------- ---- --------------------00:00:00:0A:00:0B 17.16.0.1 infinite static 10 FastEthernet6/10Table 16 describes the significant fields in the display.
Related Commands
show ip verify source
To display the IP source guard configuration and filters on a particular interface, use the show ip verify source command.
show ip verify source [interface type mod/port]
Syntax Description
Defaults
This command has no default settings.
Command Modes
Privileged EXEC
Command History
Usage Guidelines
Enable port security first because the DHCP security MAC filter cannot apply to the port or VLAN.
Examples
This example shows the display when DHCP snooping is enabled on VLANs 10-20, the interface has IP source filter mode that is configured as IP, and there is an existing IP address binding 10.0.0.1 on VLAN 10:
Router# show ip verify source interface gigabitethernet6/1Interface Filter-type Filter-mode IP-address Mac-address Vlan--------- ----------- ----------- --------------- -------------- ---------gi6/1 ip active 10.0.0.1 10gi6/1 ip active deny-all 11-20This example shows how to display the IP source guard configuration and filters on a specific interface:
Router# show ip verify source interface gigabitethernet6/1Interface Filter-type Filter-mode IP-address Mac-address Vlan--------- ----------- ----------- --------------- -------------- ---------gi6/1 ip inactive-trust-portThis example shows the display when the interface does not have a VLAN enabled for DHCP snooping:
Router# show ip verify source interface gigabitethernet6/3Interface Filter-type Filter-mode IP-address Mac-address Vlan--------- ----------- ----------- --------------- -------------- ---------gi6/3 ip inactive-no-snooping-vlanThis example shows the display when the interface has an IP source filter mode that is configured as IP MAC and the existing IP MAC that binds 10.0.0.2/aaaa.bbbb.cccc on VLAN 10 and 10.0.0.1/aaaa.bbbb.cccd on VLAN 11:
Router# show ip verify source interface gigabitethernet6/4Interface Filter-type Filter-mode IP-address Mac-address Vlan--------- ----------- ----------- --------------- -------------- ---------gi6/4 ip-mac active 10.0.0.2 aaaa.bbbb.cccc 10gi6/4 ip-mac active 10.0.0.1 aaaa.bbbb.cccd 11gi6/4 ip-mac active deny-all deny-all 12-20This example shows the display when the interface has an IP source filter mode that is configured as IP MAC and existing IP MAC binding 10.0.0.3/aaaa.bbbb.ccce on VLAN 10, but port security is not enabled on the interface:
Router# show ip verify source interface gigabitethernet6/5Interface Filter-type Filter-mode IP-address Mac-address Vlan--------- ----------- ----------- --------------- -------------- ---------gi6/5 ip-mac active 10.0.0.3 permit-all 10gi6/5 ip-mac active deny-all permit-all 11-20This example shows the display when the interface does not have IP source filter mode that is configured:
Router# show ip verify source interface gigabitethernet6/6DHCP security is not configured on the interface gi6/6.This example shows how to display all the interfaces on the switch that have DHCP snooping security enabled:
Router# show ip verify sourceInterface Filter-type Filter-mode IP-address Mac-address Vlan--------- ----------- ----------- --------------- -------------- ---------gi6/1 ip active 10.0.0.1 10gi6/1 ip active deny-all 11-20gi6/2 ip inactive-trust-portgi6/3 ip inactive-no-snooping-vlangi6/4 ip-mac active 10.0.0.2 aaaa.bbbb.cccc 10gi6/4 ip-mac active 11.0.0.1 aaaa.bbbb.cccd 11gi6/4 ip-mac active deny-all deny-all 12-20gi6/5 ip-mac active 10.0.0.3 permit-all 10gi6/5 ip-mac active deny-all permit-all 11-20Router#Related Commands
term ip netmask-format
To specify the format in which netmasks are displayed in show command output, use the term ip netmask-format command in EXEC configuration mode. To restore the default display format, use the no form of this command.
term ip netmask-format {bitcount | decimal | hexadecimal}
no term ip netmask-format [bitcount | decimal | hexadecimal]
Syntax Description
bitcount
Number of bits in the netmask.
decimal
Netmask dotted decimal notation.
hexadecimal
Netmask hexadecimal format.
Defaults
Netmasks are displayed in dotted decimal format.
Command Modes
EXEC
Command History
Usage Guidelines
IP uses a 32-bit mask that indicates which address bits belong to the network and subnetwork fields, and which bits belong to the host field. This range of IP addresses is called a netmask. By default, show commands display an IP address and then its netmask in dotted decimal notation. For example, a subnet would be displayed as 131.108.11.55 255.255.255.0.
However, you can specify that the display of the network mask appear in hexadecimal format or bit count format instead. The hexadecimal format is commonly used on UNIX systems. The previous example would be displayed as 131.108.11.55 0XFFFFFF00.
The bitcount format for displaying network masks is to append a slash (/) and the total number of bits in the netmask to the address itself. The previous example would be displayed as 131.108.11.55/24.
Examples
The following example specifies that network masks for the session be displayed in bitcount notation in the output of show commands:
term ip netmask-format bitcount
