The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.
The Network Stack IPv4 and IPv6 features are used to configure and monitor Internet Protocol Version 4 (IPv4) and Internet Protocol Version 6 (IPv6).
Restrictions
In any Cisco IOS XR software release with IPv6 support, multiple IPv6 global addresses can be configured on an interface. However, multiple IPv6 link-local addresses on an interface are not supported.
The Network Stack feature in the Cisco IOS XR software has the following exceptions:
In Cisco IOS XR software, the clear ipv6 neighbors and show ipv6 neighbors commands include the location node-id keyword. If a location is specified, only the neighbor entries in the specified location are displayed.
The ipv6 nd scavenge-timeout command sets the lifetime for neighbor entries in the stale state. When the scavenge-timer for a neighbor entry expires, the entry is cleared.
In Cisco IOS XR software, the show ipv4 interface and show ipv6 interface commands include the location node-id keyword. If a location is specified, only the interface entries in the specified location are displayed.
Cisco IOS XR software allows conflicting IP address entries at the time of configuration. If an IP address conflict exists between two interfaces that are active, Cisco IOS XR software brings down the interface according to the configured conflict policy, the default policy being to bring down the higher interface instance. For example, if HundredGigE 0/0/0/1 conflicts with HundredGigE 0/0/0/2, then the IPv4 protocol on HundredGigE 0/0/0/2, is brought down and IPv4 remains active on HundredGigE 0/0/0/1.
When Cisco IOS XR software is configured with both an IPv4 and an IPv6 address, the interface can send and receive data on both IPv4 and IPv6 networks.
The architecture of IPv6 has been designed to allow existing IPv4 users to make the transition easily to IPv6 while providing services such as end-to-end security, quality of service (QoS), and globally unique addresses. The larger IPv6 address space allows networks to scale and provide global reachability. The simplified IPv6 packet header format handles packets more efficiently. IPv6 prefix aggregation, simplified network renumbering, and IPv6 site multihoming capabilities provide an IPv6 addressing hierarchy that allows for more efficient routing. IPv6 supports widely deployed routing protocols such as Open Shortest Path First (OSPF), and multiprotocol Border Gateway Protocol (BGP).
IPv6, formerly named IPng (next generation) is the latest version of the Internet Protocol (IP). IP is a packet-based protocol used to exchange data, voice, and video traffic over digital networks. IPv6 was proposed when it became clear that the 32-bit addressing scheme of IP version 4 (IPv4) was inadequate to meet the demands of Internet growth. After extensive discussion, it was decided to base IPng on IP but add a much larger address space and improvements such as a simplified main header and extension headers. IPv6 is described initially in RFC 2460, Internet Protocol, Version 6 (IPv6) Specification issued by the Internet Engineering Task Force (IETF). Further RFCs describe the architecture and services supported by IPv6.
You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.
This section contains the following procedures:
A basic and required task for configuring IP is to assign IPv4 addresses to network interfaces. Doing so enables the interfaces and allows communication with hosts on those interfaces using IPv4. An IP address identifies a location to which IP datagrams can be sent. An interface can have one primary IP address and multiple secondary addresses. Packets generated by the software always use the primary IPv4 address. Therefore, all networking devices on a segment should share the same primary network number.
Associated with this task are decisions about subnetting and masking the IP addresses. A mask identifies the bits that denote the network number in an IP address. When you use the mask to subnet a network, the mask is then referred to as a subnet mask.
 Note |
Cisco supports only network masks that use contiguous bits that are flush left against the network field. |
An IPv4 address of 192.0.2.27 and a network mask of "/24" is assigned to the interface HundredGigE 0/0/0/24.
Note |
The network mask can be a four-part dotted decimal address. For example, 255.255.255.0 indicates that each bit equal to 1 means the corresponding address bit belongs to the network address. The network mask can be indicated as a slash (/) and a number- a prefix length. The prefix length is a decimal value that indicates how many of the high-order contiguous bits of the address comprise the prefix (the network portion of the address). A slash must precede the decimal value, and there is no space between the IP address and the slash. |
Router#configure
Router(config)#interface HundredGigE 0/0/0/24
Router(config-if)#ipv4 address 192.0.2.27/24
Router(config-if)#no shutdown
Router(config-if)#commitRouter#show running-config interface HundredGigE 0/0/0/24
interface HundredGigE0/0/0/24
ipv4 address 192.0.2.27 255.255.255.0
!Verify that the HundredGigE interface is active and IPv4 is enabled..
Router# show ipv4 interface HundredGigE 0/0/0/24
Fri Sep 27 09:36:36.244 UTC
HundredGigE0/0/0/24 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is 192.0.2.27/24
MTU is 1514 (1500 is available to IP)
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000Configuring an IPv4 virtual address enables you to access the router from a single virtual address with a management network, without the prior knowledge of which route processor (RP) is active. An IPv4 virtual address persists across RP failover situations. For this to happen, the virtual IPv4 address must share a common IPv4 subnet with a Management Ethernet interface on both RPs.
The vrf keyword supports virtual addresses on a per-VRF basis.
The use-as-src-addr keyword eliminates the need for configuring a loopback interface as the source interface (that is, update source) for management applications. When an update source is not configured, management applications allow the transport processes (TCP, UDP, raw_ip) to select a suitable source address. The transport processes, in turn, consult the FIB for selecting a suitable source address. If a Management Ethernet's IP address is selected as the source address and if the use-as-src-addr keyword is configured, then the transport substitutes the Management Ethernet's IP address with a relevant virtual IP address. This functionality works across RP switchovers. If the use-as-src-addr is not configured, then the source-address selected by transports can change after a failover and the NMS software may not be able to manage this situation.
Note |
Protocol configuration such as tacacs source-interface, snmp-server trap-source, ntp source, logging source-interface do not use the virtual management IP address as their source by default. Use the ipv4 virtual address use-as-src-addr command to ensure that the protocol uses the virtual IPv4 address as its source address. Alternatively, you can also configure a loopback address with the designated or desired IPv4 address and set that as the source for protocols such as TACACS+ via the tacacs source-interface command. |
The following example shows how to define an IPv4 virtual address:
Router#configure terminal
Router(config)#ipv4 virtual address 192.0.2.28/24
Router(config-if)#commitThe following example shows how to define an IPv4 virtual address on a management interface:
Router#configure terminal
Router(config)#ipv4 virtual address 192.0.2.28/24
Router(config)#interface mgmtEth 0/RP0/CPU0/0
Router(config-if)#ipv4 address 192.0.2.28/24
Router(config-if)#no shut
Router(config-if)#commit
Router(config-if)#exitRouter#show running-config interface mgmtEth 0/RP0/CPU0/0
Fri Sep 27 09:55:08.173 UTC
interface MgmtEth0/RP0/CPU0/0
ipv4 address 192.0.2.28 255.255.255.0
!
The following example show how to configure the virtual IP addresses for management interfaces on a per VRF basis:
Router#configure terminal
Router(config)#interface mgmtEth 0/RP0/CPU0/0
Router(config)#VRF test
Router(config-if)#ipv4 address 192.0.2.29 2555.255.255.0
Router(config-if)#no shutdown
Router(config-if)#commit
Router#show running-config interface mgmtEth 0/RP0/CPU0/0
Fri Sep 27 10:32:45.932 UTC
interface MgmtEth0/RP0/CPU0/0
vrf test
ipv4 address 192.0.2.29 255.255.255.0
!
The IPv4 ICMP rate limiting feature limits the rate that IPv4 ICMP destination unreachable messages are generated. The Cisco IOS XR software maintains two timers: one for general destination unreachable messages and one for DF destination unreachable messages. Both share the same time limits and defaults. If the DF keyword is not configured, the icmp ipv4 rate-limit unreachable command sets the time values for DF destination unreachable messages. If the DF keyword is configured, its time values remain independent from those of general destination unreachable messages.
Limits the rate that IPv4 ICMP destination unreachable messages are generated every 1000 millisecond.
The DF keyword, which is optional limits the rate at which ICMP destination unreachable messages are sent when code 4 fragmentation is needed and Don't Fragment (DF) is set, as specified in the IP header of the ICMP destination unreachable message.
Router#configure
Router(config)#icmp ipv4 rate-limit unreachable 1000
Router(config)#icmp ipv4 rate-limit unreachable DF 1000
Router(config)#commitRouter#show running-config | in icmp
Building configuration...
icmp ipv4 rate-limit unreachable DF 1000
icmp ipv4 rate-limit unreachable 1000Router#show ipv4 interface HundredGigE0/0/0/2
HundredGigE0/0/0/2 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is 192.85.1.1/24
MTU is 1514 (1500 is available to IP)
Helper address is not set
Multicast reserved groups joined: 224.0.0.2 224.0.0.1 224.0.0.2
224.0.0.5 224.0.0.6
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000The number of ICMP unreachable messages that were we sent or received can be identified using the show ipv4 traffic command.
Router# show ipv4 traffic
ICMP statistics:
Sent: 0 admin unreachable, 5 network unreachable
0 host unreachable, 0 protocol unreachable
0 port unreachable, 0 fragment unreachable
0 time to live exceeded, 0 reassembly ttl exceeded
0 echo request, 0 echo reply
0 mask request, 0 mask reply
0 parameter error, 0 redirects
5 total
Rcvd: 0 admin unreachable, 0 network unreachable
0 host unreachable, 0 protocol unreachable
0 port unreachable, 0 fragment unreachable
0 time to live exceeded, 0 reassembly ttl exceeded
0 echo request, 0 echo reply
0 mask request, 0 mask reply
0 redirect, 0 parameter error
0 source quench, 0 timestamp, 0 timestamp reply
0 router advertisement, 0 router solicitation
0 total, 0 checksum errors, 0 unknownThis section describes the process of enabling an IPv4 point-to-point interface without assigning an explicit IP address to the interface. Whenever the unnumbered interface generates a packet (for example, for a routing update), it uses the address of the interface you specified as the source address of the IP packet. It also uses the specified interface address in determining which routing processes are sending updates over the unnumbered interface. Restrictions are as follows:
You cannot use the ping EXEC command to determine whether the interface is up, because the interface has no IP address. The Simple Network Management Protocol (SNMP) can be used to remotely monitor interface status.
You cannot support IP security options on an unnumbered interface.
Enables an IPv4 point-to-point interface without assigning an explicit IP address to the interface.
Router#configure
Router(config)#interface HundredGigE 0/0/0/25
Router(config-if)#ipv4 point-to-point
Router(config-if)#commit
Router(config-if)#ipv4 unnumbered loopback 0
Router(config-if)#commitRouter#show running-config interface HundredGigE 0/0/0/25
interface HundredGigE0/0/0/25
ipv4 point-to-point
ipv4 unnumbered Loopback0
!Router#show interface HundredGigE 0/0/0/25
HundredGigE0/0/0/25 is up, line protocol is up
Interface state transitions: 5
Hardware is HundredGigE, address is 00e2.2a33.445b (bia 00e2.2a33.445b)
Layer 1 Transport Mode is LAN
Internet address is 192.0.2.1/24
MTU 1514 bytes, BW 10000000 Kbit (Max: 10000000 Kbit)
reliability 255/255, txload 194/255, rxload 0/255
Encapsulation ARPA,
Full-duplex, 10000Mb/s, link type is force-up
output flow control is off, input flow control is off
Carrier delay (up) is 10 msec
loopback not set,
Last link flapped 01:38:49
ARP type ARPA, ARP timeout 04:00:00
Last input 00:00:00, output 00:00:00
Last clearing of "show interface" counters 02:34:16
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 7647051000 bits/sec, 12254894 packets/sec
1061401410 packets input, 82789675614 bytes, 0 total input drops
0 drops for unrecognized upper-level protocol
Received 5 broadcast packets, 19429 multicast packets
0 runts, 0 giants, 0 throttles, 0 parity
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
76895885948 packets output, 6192569128048 bytes, 0 total output drops
Output 7 broadcast packets, 18916 multicast packets
0 output errors, 0 underruns, 0 applique, 0 resets
0 output buffer failures, 0 output buffers swapped out
2 carrier transitions
Router #show runnning-config interface loopback 0
interface Loopback0
ipv4 address 192.0.2.1 255.255.255.255The Cisco IOS XR software supports multiple IP addresses (secondary addresses) per interface. You can specify an unlimited number of secondary addresses. Secondary IP addresses can be used in a variety of situations. The following are the most common applications:
There might not be enough host addresses for a particular network segment. For example, suppose your subnetting allows up to 254 hosts per logical subnet, but on one physical subnet you must have 300 host addresses. Using secondary IP addresses on the routers or access servers allows you to have two logical subnets using one physical subnet.
Many older networks were built using Level 2 bridges, and were not subnetted. The judicious use of secondary addresses can aid in the transition to a subnetted, router-based network. Routers on an older, bridged segment can easily be made aware that many subnets are on that segment.
Two subnets of a single network might otherwise be separated by another network. You can create a single network from subnets that are physically separated by another network by using a secondary address. In these instances, the first network is extended, or layered on top of the second network. Note that a subnet cannot appear on more than one active interface of the router at a time.
Note |
If any router on a network segment uses a secondary IPv4 address, all other routers on that same segment must also use a secondary address from the same network or subnet. |
 Caution |
Inconsistent use of secondary addresses on a network segment can quickly cause routing loops. |
A secondary IPv4 address of 192.0.2.1 is assigned to the Hundredgige interface-0/0/0/24.
Note: For IPv6, an interface can have multiple IPv6 addresses without specifying the secondary keyword.
Router#configure
Router(config)#interface HundredGigE 0/0/0/24
Router(config-if)#ipv4 address 192.0.2.1 255.255.255.0 secondary
Router(config-if)#commitRouter#show running-config interface HundredGigE 0/0/0/24
Mon Sep 30 09:37:12.096 UTC
interface HundredGigE0/0/0/24
ipv4 address 192.0.2.27 255.255.255.0
ipv4 address 192.0.2.1 255.255.255.0 secondary
!Router#show ipv4 interface HundredGigE 0/0/0/24
Mon Sep 30 09:38:18.262 UTC
HundredGigE0/0/0/24 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is 192.0.2.27/24
Secondary address 192.0.2.1/24
MTU is 1514 (1500 is available to IP)
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000IPv6 addresses are configured to individual router interfaces in order to enable the forwarding of IPv6 traffic globally on the router. By default, IPv6 addresses are not configured.
Note |
The ipv6-prefix argument in the ipv6 address command must be in the form documented in RFC 2373 in which the address is specified in hexadecimal using 16-bit values between colons. |
The /prefix-length argument in the ipv6 address command is a decimal value that indicates how many of the high-order contiguous bits of the address comprise the prefix (the network portion of the address) A slash must precede the decimal value.
The ipv6-address argument in the ipv6 address link-local command must be in the form documented in RFC 2373 where the address is specified in hexadecimal using 16-bit values between colons.
The primary motivation for IPv6 is the need to meet the anticipated future demand for globally unique IP addresses. Applications such as mobile Internet-enabled devices (such as personal digital assistants [PDAs], telephones, and cars), home-area networks (HANs), and wireless data services are driving the demand for globally unique IP addresses. IPv6 quadruples the number of network address bits from 32 bits (in IPv4) to 128 bits, which provides more than enough globally unique IP addresses for every networked device on the planet. By being globally unique, IPv6 addresses inherently enable global reachability and end-to-end security for networked devices, functionality that is crucial to the applications and services that are driving the demand for the addresses. Additionally, the flexibility of the IPv6 address space reduces the need for private addresses and the use of Network Address Translation (NAT); therefore, IPv6 enables new application protocols that do not require special processing by border routers at the edge of networks.
IPv6 addresses are represented as a series of 16-bit hexadecimal fields separated by colons (:) in the format: x:x:x:x:x:x:x:x. Following are two examples of IPv6 addresses:
2001:0DB8:7654:3210:FEDC:BA98:7654:3210
2001:0DB8:0:0:8:800:200C:417A
It is common for IPv6 addresses to contain successive hexadecimal fields of zeros. To make IPv6 addresses less cumbersome, two colons (::) can be used to compress successive hexadecimal fields of zeros at the beginning, middle, or end of an IPv6 address. (The colons represent successive hexadecimal fields of zeros.) Table 1 lists compressed IPv6 address formats.
A double colon may be used as part of the ipv6-address argument when consecutive 16-bit values are denoted as zero. You can configure multiple IPv6 addresses per interfaces, but only one link-local address.
Note |
Two colons (::) can be used only once in an IPv6 address to represent the longest successive hexadecimal fields of zeros. |
The hexadecimal letters in IPv6 addresses are not case-sensitive.
|
IPv6 Address Type |
Preferred Format |
Compressed Format |
|---|---|---|
|
Unicast |
2001:0:0:0:0DB8:800:200C:417A |
1080::0DB8:800:200C:417A |
|
Multicast |
FF01:0:0:0:0:0:0:101 |
FF01::101 |
|
Loopback |
0:0:0:0:0:0:0:1 |
::1 |
|
Unspecified |
0:0:0:0:0:0:0:0 |
:: |
The loopback address listed in Table 1 may be used by a node to send an IPv6 packet to itself. The loopback address in IPv6 functions the same as the loopback address in IPv4 (127.0.0.1).
Note |
The IPv6 loopback address cannot be assigned to a physical interface. A packet that has the IPv6 loopback address as its source or destination address must remain within the node that created the packet. IPv6 routers do not forward packets that have the IPv6 loopback address as their source or destination address. |
The unspecified address listed in Table 1 indicates the absence of an IPv6 address. For example, a newly initialized node on an IPv6 network may use the unspecified address as the source address in its packets until it receives its IPv6 address.
Note |
The IPv6 unspecified address cannot be assigned to an interface. The unspecified IPv6 addresses must not be used as destination addresses in IPv6 packets or the IPv6 routing header. |
An IPv6 address prefix, in the format ipv6-prefix/prefix-length , can be used to represent bit-wise contiguous blocks of the entire address space. The ipv6-prefix argument must be in the form documented in RFC 2373, in which the address is specified in hexadecimal using 16-bit values between colons. The prefix length is a decimal value that indicates how many of the high-order contiguous bits of the address compose the prefix (the network portion of the address). For example, 2001:0DB8:8086:6502::/32 is a valid IPv6 prefix.
An IPv6 unicast address is an identifier for a single interface, on a single node. A packet that is sent to a unicast address is delivered to the interface identified by that address. Cisco IOS XR software supports the following IPv6 unicast address types:
Global aggregatable address
Site-local address (proposal to remove by IETF)
Link-local address
IPv4-compatible IPv6 address
An aggregatable global address is an IPv6 address from the aggregatable global unicast prefix. The structure of aggregatable global unicast addresses enables strict aggregation of routing prefixes that limits the number of routing table entries in the global routing table. Aggregatable global addresses are used on links that are aggregated upward through organizations, and eventually to the Internet service providers (ISPs).
Aggregatable global IPv6 addresses are defined by a global routing prefix, a subnet ID, and an interface ID. Except for addresses that start with binary 000, all global unicast addresses have a 64-bit interface ID. The current global unicast address allocation uses the range of addresses that start with binary value 001 (2000::/3). This figure below shows the structure of an aggregatable global address.
Addresses with a prefix of 2000::/3 (001) through E000::/3 (111) are required to have 64-bit interface identifiers in the extended universal identifier (EUI)-64 format. The Internet Assigned Numbers Authority (IANA) allocates the IPv6 address space in the range of 2000::/16 to regional registries.
The aggregatable global address typically consists of a 48-bit global routing prefix and a 16-bit subnet ID or Site-Level Aggregator (SLA). In the IPv6 aggregatable global unicast address format document (RFC 2374), the global routing prefix included two other hierarchically structured fields named Top-Level Aggregator (TLA) and Next-Level Aggregator (NLA).The IETF decided to remove the TLS and NLA fields from the RFCs, because these fields are policy-based. Some existing IPv6 networks deployed before the change might still be using networks based on the older architecture.
A 16-bit subnet field called the subnet ID could be used by individual organizations to create their own local addressing hierarchy and to identify subnets. A subnet ID is similar to a subnet in IPv4, except that an organization with an IPv6 subnet ID can support up to 65,535 individual subnets.
An interface ID is used to identify interfaces on a link. The interface ID must be unique to the link. It may also be unique over a broader scope. In many cases, an interface ID is the same as or based on the link-layer address of an interface. Interface IDs used in aggregatable global unicast and other IPv6 address types must be 64 bits long and constructed in the modified EUI-64 format.
Interface IDs are constructed in the modified EUI-64 format in one of the following ways:
For all IEEE 802 interface types (for example, Ethernet interfaces and FDDI interfaces), the first three octets (24 bits) are taken from the Organizationally Unique Identifier (OUI) of the 48-bit link-layer address (MAC address) of the interface, the fourth and fifth octets (16 bits) are a fixed hexadecimal value of FFFE, and the last three octets (24 bits) are taken from the last three octets of the MAC address. The construction of the interface ID is completed by setting the Universal/Local (U/L) bit—the seventh bit of the first octet—to a value of 0 or 1. A value of 0 indicates a locally administered identifier; a value of 1 indicates a globally unique IPv6 interface identifier.
For tunnel interface types that are used with IPv6 overlay tunnels, the interface ID is the IPv4 address assigned to the tunnel interface with all zeros in the high-order 32 bits of the identifier.
Note |
For interfaces using Point-to-Point Protocol (PPP), given that the interfaces at both ends of the connection might have the same MAC address, the interface identifiers used at both ends of the connection are negotiated (picked randomly and, if necessary, reconstructed) until both identifiers are unique. The first MAC address in the router is used to construct the identifier for interfaces using PPP. |
If no IEEE 802 interface types are in the router, link-local IPv6 addresses are generated on the interfaces in the router in the following sequence:
The router is queried for MAC addresses (from the pool of MAC addresses in the router).
If no MAC address is available, the serial number of the Route Processor (RP) or line card (LC) is used to form the link-local address.
A link-local address is an IPv6 unicast address that can be automatically configured on any interface using the link-local prefix FE80::/10 (1111 1110 10) and the interface identifier in the modified EUI-64 format. Link-local addresses are used in the neighbor discovery protocol and the stateless autoconfiguration process. Nodes on a local link can use link-local addresses to communicate; the nodes do not need site-local or globally unique addresses to communicate. This figure below shows the structure of a link-local address.
IPv6 routers must not forward packets that have link-local source or destination addresses to other links.
An IPv4-compatible IPv6 address is an IPv6 unicast address that has zeros in the high-order 96 bits of the address and an IPv4 address in the low-order 32 bits of the address. The format of an IPv4-compatible IPv6 address is 0:0:0:0:0:0:A.B.C.D or ::A.B.C.D. The entire 128-bit IPv4-compatible IPv6 address is used as the IPv6 address of a node and the IPv4 address embedded in the low-order 32 bits is used as the IPv4 address of the node. IPv4-compatible IPv6 addresses are assigned to nodes that support both the IPv4 and IPv6 protocol stacks and are used in automatic tunnels. This figure below shows the structure of an IPv4-compatible IPv6 address and a few acceptable formats for the address.
The basic IPv4 packet header has 12 fields with a total size of 20 octets (160 bits). The 12 fields may be followed by an Options field, which is followed by a data portion that is usually the transport-layer packet. The variable length of the Options field adds to the total size of the IPv4 packet header. The shaded fields of the IPv4 packet header are not included in the IPv6 packet header.
The basic IPv6 packet header has 8 fields with a total size of 40 octets (320 bits). Fields were removed from the IPv6 header because, in IPv6, fragmentation is not handled by routers and checksums at the network layer are not used. Instead, fragmentation in IPv6 is handled by the source of a packet and checksums at the data link layer and transport layer are used. (In IPv4, the User Datagram Protocol (UDP) transport layer uses an optional checksum. In IPv6, use of the UDP checksum is required to check the integrity of the inner packet.) Additionally, the basic IPv6 packet header and Options field are aligned to 64 bits, which can facilitate the processing of IPv6 packets.
This table lists the fields in the basic IPv6 packet header.
|
Field |
Description |
|---|---|
|
Version |
Similar to the Version field in the IPv4 packet header, except that the field lists number 6 for IPv6 instead of number 4 for IPv4. |
|
Traffic Class |
Similar to the Type of Service field in the IPv4 packet header. The Traffic Class field tags packets with a traffic class that is used in differentiated services. |
|
Flow Label |
A new field in the IPv6 packet header. The Flow Label field tags packets with a specific flow that differentiates the packets at the network layer. |
|
Payload Length |
Similar to the Total Length field in the IPv4 packet header. The Payload Length field indicates the total length of the data portion of the packet. |
|
Next Header |
Similar to the Protocol field in the IPv4 packet header. The value of the Next Header field determines the type of information following the basic IPv6 header. The type of information following the basic IPv6 header can be a transport-layer packet, for example, a TCP or UDP packet, or an Extension Header. |
|
Hop Limit |
Similar to the Time to Live field in the IPv4 packet header. The value of the Hop Limit field specifies the maximum number of routers that an IPv6 packet can pass through before the packet is considered invalid. Each router decrements the value by one. Because no checksum is in the IPv6 header, the router can decrement the value without needing to recalculate the checksum, which saves processing resources. |
|
Source Address |
Similar to the Source Address field in the IPv4 packet header, except that the field contains a 128-bit source address for IPv6 instead of a 32-bit source address for IPv4. |
|
Destination Address |
Similar to the Destination Address field in the IPv4 packet header, except that the field contains a 128-bit destination address for IPv6 instead of a 32-bit destination address for IPv4. |
Following the eight fields of the basic IPv6 packet header are optional extension headers and the data portion of the packet. If present, each extension header is aligned to 64 bits. There is no fixed number of extension headers in an IPv6 packet. Together, the extension headers form a chain of headers. Each extension header is identified by the Next Header field of the previous header. Typically, the final extension header has a Next Header field of a transport-layer protocol, such as TCP or UDP. This figure below shows the IPv6 extension header format.
This table lists the extension header types and their Next Header field values.
|
Header Type |
Next Header Value |
Description |
|---|---|---|
|
Hop-by-hop options header |
0 |
This header is processed by all hops in the path of a packet. When present, the hop-by-hop options header always follows immediately after the basic IPv6 packet header. |
|
Destination options header |
60 |
The destination options header can follow any hop-by-hop options header, in which case the destination options header is processed at the final destination and also at each visited address specified by a routing header. Alternatively, the destination options header can follow any Encapsulating Security Payload (ESP) header, in which case the destination options header is processed only at the final destination. |
|
Routing header |
43 |
The routing header is used for source routing. |
|
Fragment header |
44 |
The fragment header is used when a source must fragment a packet that is larger than the maximum transmission unit (MTU) for the path between itself and a destination. The Fragment header is used in each fragmented packet. |
|
Authentication header and ESP header |
51 50 |
The Authentication header and the ESP header are used within IP Security Protocol (IPSec) to provide authentication, integrity, and confidentiality of a packet. These headers are identical for both IPv4 and IPv6. |
|
Upper-layer header |
6 (TCP) 17 (UDP) |
The upper-layer (transport) headers are the typical headers used inside a packet to transport the data. The two main transport protocols are TCP and UDP. |
|
Mobility header |
To be done by IANA |
Extension headers used by mobile nodes, correspondent nodes, and home agents in all messaging related to the creation and management of bindings. |
An IPv6 address must be configured on an interface for the interface to forward IPv6 traffic. Configuring a global IPv6 address on an interface automatically configures a link-local address and activates IPv6 for that interface.
Additionally, the configured interface automatically joins the following required multicast groups for that link:
Solicited-node multicast group FF02:0:0:0:0:1:FF00::/104 for each unicast address assigned to the interface
All-nodes link-local multicast group FF02::1
All-routers link-local multicast group FF02::2
Note |
The solicited-node multicast address is used in the neighbor discovery process. |
An IPv6 address of 2001:0DB8:0:1::1/64 is assigned to the HundredGigE interface 0/0/0/25:
Router# configure
Router(config)# interface HundredGigE 0/0/0/25
Router(config-if)# ipv6 address 2001:0DB8:0:1::1/64
Router(config-if)# no shutdown
Router(config-if)#commitRouter# show running-config interface HundredGigE 0/0/0/25
interface HundredGigE0/0/0/25
ipv6 address 2001:db8:0:1::1/64
!Verify that the HundredGigE interface is active and IPv6 is enabled.
Router#show ipv6 interface HundredGigE 0/0/0/25
HundredGigE0/0/0/25 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::7ae7:abff:febd:d4c4
Global unicast address(es):
2001:db8:0:1::1, subnet is 2001:db8:0:1::/64
2001:db8:0:1:7ae7:abff:febd:d4c4, subnet is 2001:db8:0:1::/64
Joined group address(es): ff02::1:ff00:1 ff02::1:ffbd:d4c4 ff02::2
ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 160 to 240 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0An IPv6 address of 2001:0DB8:0:1::/64 is assigned to the interface HundredGigE 0/0/0/35. The eui-64 keyword configures site-local and global IPv6 addresses with an interface identifier (ID) in the low-order 64 bits of the IPv6 address. Only the 64-bit network prefix for the address needs to be specified; the last 64 bits are automatically computed from the interface ID.
Router# configure
Router(config)# interface HundredGigE 0/0/0/35
Router(config-if)# ipv6 address 2001:0DB8:0:1::/64 eui-64
Router(config-if)#no shutdown
Router(config-if)#commitRouter# show running-config interface HundredGigE 0/0/0/35
Mon Sep 30 09:05:07.715 UTC
interface HundredGigE0/0/0/35
ipv6 address 2001:db8:0:1::/64 eui-64
!
Router#show ipv6 interface HundredGigE 0/0/0/35
Mon Sep 30 09:06:12.638 UTC
HundredGigE0/0/0/35 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::7ae7:abff:febd:d4ec
Global unicast address(es):
2001:db8:0:1:7ae7:abff:febd:d4ec, subnet is 2001:db8:0:1::/64
Joined group address(es): ff02::1:ffbd:d4ec ff02::2 ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 160 to 240 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0An IPv6 address of FE80::260:3EFF:FE11:6770 is assigned to the interface HundredGigE 0/0/0/34. The link-local keyword configures a link-local address on the interface that is used instead of the link-local address that is automatically configured when IPv6 is enabled on the interface.
Router#configure
Router(config)#interface HundredGigE 0/0/0/34
Router(config-if)#ipv6 address FE80::260:3EFF:FE11:6770 link-local
Router(config-if)#no shutdown
Router(config-if)#commitRouter# show running-config interface HundredGigE 0/0/0/34
Mon Sep 30 09:11:09.742 UTC
interface HundredGigE0/0/0/34
ipv6 address fe80::260:3eff:fe11:6770 link-local
!Verify that the HundredGigE interface is active and IPv6 is enabled with link-local address.
Router#show ipv6 interface HundredGigE 0/0/0/34
HundredGigE0/0/0/34 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::260:3eff:fe11:6770
No global unicast address is configured
Joined group address(es): ff02::1:ff11:6770 ff02::2 ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 160 to 240 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0Router#configure
Router(config)#interface HundredGigE 0/0/0/33
Router(config-if)#ipv6 enable
Router(config-if)#no shutdown
Router(config-if)#commitRouter#show running-config interface HundredGigE 0/0/0/33
Mon Sep 30 09:14:03.623 UTC
interface HundredGigE0/0/0/33
ipv6 enable
!Router#show ipv6 interface HundredGigE 0/0/0/33
Mon Sep 30 09:14:48.430 UTC
HundredGigE0/0/0/33 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::7ae7:abff:febd:d4e4
No global unicast address is configured
Joined group address(es): ff02::1:ffbd:d4e4 ff02::2 ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 160 to 240 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0Configuring an IPv6 virtual address enables you to access the router from a single virtual address with a management network, without the prior knowledge of which route processor (RP) is active. An IPv6 virtual address persists across RP failover situations. For this to happen, the virtual IPv6 address must share a common IPv6 subnet with a Management Ethernet interface on both RPs.
The vrf keyword supports virtual addresses on a per-VRF basis.
The use-as-src-addr keyword eliminates the need for configuring a loopback interface as the source interface (that is, update source) for management applications. When an update source is not configured, management applications allow the transport processes (TCP, UDP, raw_ip) to select a suitable source address. The transport processes, in turn, consult the FIB for selecting a suitable source address. If a Management Ethernet's IP address is selected as the source address and if the use-as-src-addr keyword is configured, then the transport substitutes the Management Ethernet's IP address with a relevant virtual IP address. This functionality works across RP switchovers. If the use-as-src-addr is not configured, then the source-address selected by transports can change after a failover and the NMS software may not be able to manage this situation.
Note |
Protocol configuration such as tacacs source-interface, snmp-server trap-source, ntp source, logging source-interface do not use the virtual management IP address as their source by default. Use the ipv6 virtual address use-as-src-addr command to ensure that the protocol uses the virtual IPv6 address as its source address. Alternatively, you can also configure a loopback address with the designated or desired IPv6 address and set that as the source for protocols such as TACACS+ via the tacacs source-interface command. |
The following example shows how to define an IPv6 virtual address:
Router#configure terminal
Router(config)#ipv6 virtual address 2001:0DB8:0:1::1/64
Router(config-if)#commitThe following example shows how to define an IPv6 virtual address on a management interface:
Router#configure terminal
Router(config)#ipv6 virtual address 2001:db8:0:1::1/64
Router(config)#interface mgmtEth 0/RP0/CPU0/0
Router(config-if)#ipv6 address 2001:0DB8:0:1::1/64
Router(config-if)#no shutdown
Router(config-if)#commit
Router(config-if)#exitRouter#show running-config interface mgmtEth 0/RP0/CPU0/0
Mon Sep 30 09:18:50.468 UTC
interface MgmtEth0/RP0/CPU0/0
ipv6 address 2001:db8:0:1::1/64
!
The following example show how to configure the virtual IP addresses for management interfaces on a per VRF basis:
Router#configure terminal
Router(config)#ipv6 virtual address vrf Test 2001:0DB8:0:1::1/64
Router(config)#interface mgmtEth 0/RP0/CPU0/0
Router(config-if)#ipv6 address 2001:0DB8:0:1::1/64
Router(config-if)#no shutdown
Router(config-if)#commit
Router#show running-config interface mgmtEth 0/RP0/CPU0/0
Mon Sep 30 09:24:19.111 UTC
interface MgmtEth0/RP0/CPU0/0
ipv6 address 2001:db8:0:1::1/64
!
The IPv6 ICMP rate limiting feature implements a token bucket algorithm for limiting the rate at which IPv6 ICMP error messages are sent out on the network. The initial implementation of IPv6 ICMP rate limiting defined a fixed interval between error messages, but some applications, such as traceroute, often require replies to a group of requests sent in rapid succession. The fixed interval between error messages is not flexible enough to work with applications such as traceroute and can cause the application to fail. Implementing a token bucket scheme allows a number of tokens-representing the ability to send one error message each-to be stored in a virtual bucket. The maximum number of tokens allowed in the bucket can be specified, and for every error message to be sent, one token is removed from the bucket. If a series of error messages is generated, error messages can be sent until the bucket is empty. When the bucket is empty of tokens, IPv6 ICMP error messages are not sent until a new token is placed in the bucket. The token bucket algorithm does not increase the average rate limiting time interval, and it is more flexible than the fixed time interval scheme.
Configure the interval for 50 milliseconds and the bucket size for 20 tokens, for IPv6 ICMP error messages.
The milliseconds argument specifies the interval between tokens being added to the bucket.
The optional bucketsize argument defines the maximum number of tokens stored in the bucket.
Router#configure
Router(config)#ipv6 icmp error-interval 50 20
Router(config)#commitRouter#show running-config
Building configuration...
!! IOS XR Configuration version = 6.0.0.26I
!! Last configuration change at Mon Dec 14 22:07:35 2015 by root
!
hostname test-83
logging console debugging
username root
group root-lr
group cisco-support
secret 5 $1$d2NC$RbAdqdU7kw/kEJoMP/IJG1
!
cdp
ipv6 icmp error-interval 50 20
icmp ipv4 rate-limit unreachable DF 1000
icmp ipv4 rate-limit unreachable 1000
ipv4 conflict-policy staticipv6 icmp error-interval
This task configures an interface in a Cisco networking device to support both the IPv4 and IPv6 protocol stacks.
When an interface in a Cisco networking device is configured with both an IPv4 and an IPv6 address, the interface forwards both IPv4 and IPv6 traffic—the interface can send and receive data on both IPv4 and IPv6 networks.
An IPv4 address of 192.0.2.1 and an IPv6 address of 2001:0DB8:c18:1::3/64 is configured on the interface HundredGigE 0/0/0/31.
Router#configure
Router(config)#interface HundredGigE 0/0/0/31
Router(config-if)#ipv4 address 192.0.2.1 255.255.255.0
Router(config-if)#ipv6 address 2001:0DB8:c18:1::3/64\
Router(config-if)#no shutdown
Router(config-if)#commitRouter# show running-config interface HundredGigE 0/0/0/31
Mon Sep 30 09:45:48.379 UTC
interface HundredGigE0/0/0/31
ipv4 address 192.0.2.1 255.255.255.0
ipv6 address 2001:db8:c18:1::3/64
!Verify that the HundredGigE interface is active and IPv4 and IPv6 are enabled.
Router#show ipv4 interface HundredGigE 0/0/0/31
Mon Sep 30 09:49:10.383 UTC
HundredGigE0/0/0/31 is Up, ipv4 protocol is Up
Vrf is default (vrfid 0x60000000)
Internet address is 192.0.2.1/24
MTU is 1514 (1500 is available to IP)
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Proxy ARP is disabled
ICMP redirects are never sent
ICMP unreachables are always sent
ICMP mask replies are never sent
Table Id is 0xe0000000
Router#show ipv6 interface HundredGigE 0/0/0/31
Mon Sep 30 09:51:01.472 UTC
HundredGigE0/0/0/31 is Up, ipv6 protocol is Up, Vrfid is default (0x60000000)
IPv6 is enabled, link-local address is fe80::7ae7:abff:febd:d4dc
Global unicast address(es):
2001:db8:c18:1::3, subnet is 2001:db8:c18:1::/64
Joined group address(es): ff02::1:ff00:3 ff02::1:ffbd:d4dc ff02::2
ff02::1
MTU is 1514 (1500 is available to IPv6)
ICMP redirects are disabled
ICMP unreachables are enabled
ND DAD is enabled, number of DAD attempts 1
ND reachable time is 0 milliseconds
ND cache entry limit is 1000000000
ND advertised retransmit interval is 0 milliseconds
ND router advertisements are sent every 160 to 240 seconds
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
Outgoing access list is not set
Inbound common access list is not set, access list is not set
Table Id is 0xe0800000
Complete protocol adjacency: 0
Complete glean adjacency: 0
Incomplete protocol adjacency: 0
Incomplete glean adjacency: 0
Dropped protocol request: 0
Dropped glean request: 0
You can select flexible source IP address in the Internet Control Message Protocol (ICMP) response packet to respond to a failure.
Enables RFC compliance for source address selection.
Router#configure
Router(config)#icmp ipv4 source rfc
Router(config)#commitRouter#show running-config | in source rfc
Building configuration...
icmp ipv4 source rfcicmp ipv4 source vrf
As in IPv4, path MTU discovery in IPv6 allows a host to dynamically discover and adjust to differences in the MTU size of every link along a given data path. In IPv6, however, fragmentation is handled by the source of a packet when the path MTU of one link along a given data path is not large enough to accommodate the size of the packets. Having IPv6 hosts handle packet fragmentation saves IPv6 router processing resources and helps IPv6 networks run more efficiently.
In IPv4, the minimum link MTU is 68 octets, which means that the MTU size of every link along a given data path must support an MTU size of at least 68 octets. In IPv6, the minimum link MTU is 1280 octets. We recommend using an MTU value of 1500 octets for IPv6 links.
Note |
Path MTU discovery is supported only for applications using TCP. |
The IPv6 neighbor discovery process uses ICMP messages and solicited-node multicast addresses to determine the link-layer address of a neighbor on the same network (local link), verify the reachability of a neighbor, and keep track of neighboring routers.
A value of 135 in the Type field of the ICMP packet header identifies a neighbor solicitation message. Neighbor solicitation messages are sent on the local link when a node wants to determine the link-layer address of another node on the same local link. When a node wants to determine the link-layer address of another node, the source address in a neighbor solicitation message is the IPv6 address of the node sending the neighbor solicitation message. The destination address in the neighbor solicitation message is the solicited-node multicast address that corresponds to the IPv6 address of the destination node. The neighbor solicitation message also includes the link-layer address of the source node.
After receiving the neighbor solicitation message, the destination node replies by sending a neighbor advertisement message, which has a value of 136 in the Type field of the ICMP packet header, on the local link. The source address in the neighbor advertisement message is the IPv6 address of the node (more specifically, the IPv6 address of the node interface) sending the neighbor advertisement message. The destination address in the neighbor advertisement message is the IPv6 address of the node that sent the neighbor solicitation message. The data portion of the neighbor advertisement message includes the link-layer address of the node sending the neighbor advertisement message.
After the source node receives the neighbor advertisement, the source node and destination node can communicate.
Neighbor solicitation messages are also used to verify the reachability of a neighbor after the link-layer address of a neighbor is identified. When a node wants to verifying the reachability of a neighbor, the destination address in a neighbor solicitation message is the unicast address of the neighbor.
Neighbor advertisement messages are also sent when there is a change in the link-layer address of a node on a local link. When there is such a change, the destination address for the neighbor advertisement is the all-nodes multicast address.
Neighbor solicitation messages are also used to verify the reachability of a neighbor after the link-layer address of a neighbor is identified. Neighbor unreachability detection identifies the failure of a neighbor or the failure of the forward path to the neighbor, and is used for all paths between hosts and neighboring nodes (hosts or routers). Neighbor unreachability detection is performed for neighbors to which only unicast packets are being sent and is not performed for neighbors to which multicast packets are being sent.
A neighbor is considered reachable when a positive acknowledgment is returned from the neighbor (indicating that packets previously sent to the neighbor have been received and processed). A positive acknowledgment—from an upper-layer protocol (such as TCP)—indicates that a connection is making forward progress (reaching its destination) or that a neighbor advertisement message in response to a neighbor solicitation message has been received. If packets are reaching the peer, they are also reaching the next-hop neighbor of the source. Therefore, forward progress is also a confirmation that the next-hop neighbor is reachable.
For destinations that are not on the local link, forward progress implies that the first-hop router is reachable. When acknowledgments from an upper-layer protocol are not available, a node probes the neighbor using unicast neighbor solicitation messages to verify that the forward path is still working. The return of a solicited neighbor advertisement message from the neighbor is a positive acknowledgment that the forward path is still working. (Neighbor advertisement messages that have the solicited flag set to a value of 1 are sent only in response to a neighbor solicitation message.) Unsolicited messages confirm only the one-way path from the source to the destination node; solicited neighbor advertisement messages indicate that a path is working in both directions.
Note |
A neighbor advertisement message that has the solicited flag set to a value of 0 must not be considered as a positive acknowledgment that the forward path is still working. |
Neighbor solicitation messages are also used in the stateless autoconfiguration process to verify the uniqueness of unicast IPv6 addresses before the addresses are assigned to an interface. Duplicate address detection is performed first on a new, link-local IPv6 address before the address is assigned to an interface. (The new address remains in a tentative state while duplicate address detection is performed.) Specifically, a node sends a neighbor solicitation message with an unspecified source address and a tentative link-local address in the body of the message. If another node is already using that address, the node returns a neighbor advertisement message that contains the tentative link-local address. If another node is simultaneously verifying the uniqueness of the same address, that node also returns a neighbor solicitation message. If no neighbor advertisement messages are received in response to the neighbor solicitation message and no neighbor solicitation messages are received from other nodes that are attempting to verify the same tentative address, the node that sent the original neighbor solicitation message considers the tentative link-local address to be unique and assigns the address to the interface.
Every IPv6 unicast address (global or link-local) must be checked for uniqueness on the link; however, until the uniqueness of the link-local address is verified, duplicate address detection is not performed on any other IPv6 addresses associated with the link-local address. The Cisco implementation of duplicate address detection in the Cisco IOS XR software does not check the uniqueness of anycast or global addresses that are generated from 64-bit interface identifiers.
Router advertisement (RA) messages, which have a value of 134 in the Type field of the ICMP packet header, are periodically sent out each configured interface of an IPv6 router. The router advertisement messages are sent to the all-nodes multicast address.
Router advertisement messages typically include the following information:
One or more onlink IPv6 prefixes that nodes on the local link can use to automatically configure their IPv6 addresses
Lifetime information for each prefix included in the advertisement
Sets of flags that indicate the type of autoconfiguration (stateless or statefull) that can be completed
Default router information (whether the router sending the advertisement should be used as a default router and, if so, the amount of time, in seconds, that the router should be used as a default router)
Additional information for hosts, such as the hop limit and MTU a host should use in packets that it originates
Router advertisements are also sent in response to router solicitation messages. Router solicitation messages, which have a value of 133 in the Type field of the ICMP packet header, are sent by hosts at system startup so that the host can immediately autoconfigure without needing to wait for the next scheduled router advertisement message. Given that router solicitation messages are usually sent by hosts at system startup (the host does not have a configured unicast address), the source address in router solicitation messages is usually the unspecified IPv6 address (0:0:0:0:0:0:0:0). If the host has a configured unicast address, the unicast address of the interface sending the router solicitation message is used as the source address in the message. The destination address in router solicitation messages is the all-routers multicast address with a scope of the link. When a router advertisement is sent in response to a router solicitation, the destination address in the router advertisement message is the unicast address of the source of the router solicitation message.
The following router advertisement message parameters can be configured:
The time interval between periodic router advertisement messages
The “router lifetime” value, which indicates the usefulness of a router as the default router (for use by all nodes on a given link)
The network prefixes in use on a given link
The time interval between neighbor solicitation message retransmissions (on a given link)
The amount of time a node considers a neighbor reachable (for use by all nodes on a given link)
The configured parameters are specific to an interface. The sending of router advertisement messages (with default values) is automatically enabled on Ethernet and FDDI interfaces. For other interface types, the sending of router advertisement messages must be manually configured by using the no ipv6 nd suppress-ra command in interface configuration mode. The sending of router advertisement messages can be disabled on individual interfaces by using the ipv6 nd suppress-ra command in interface configuration mode.
Note |
For stateless autoconfiguration to work properly, the advertised prefix length in router advertisement messages must always be 64 bits. |
A value of 137 in the Type field of the ICMP packet header identifies an IPv6 neighbor redirect message. Routers send neighbor redirect messages to inform hosts of better first-hop nodes on the path to a destination.
Note |
A router must be able to determine the link-local address for each of its neighboring routers to ensure that the target address (the final destination) in a redirect message identifies the neighbor router by its link-local address. For static routing, the address of the next-hop router should be specified using the link-local address of the router; for dynamic routing, all IPv6 routing protocols must exchange the link-local addresses of neighboring routers. |
After forwarding a packet, a router should send a redirect message to the source of the packet under the following circumstances:
The destination address of the packet is not a multicast address.
The packet was not addressed to the router.
The packet is about to be sent out the interface on which it was received.
The router determines that a better first-hop node for the packet resides on the same link as the source of the packet.
The source address of the packet is a global IPv6 address of a neighbor on the same link, or a link-local address.
Use the ipv6 icmp error-interval global configuration command to limit the rate at which the router generates all IPv6 ICMP error messages, including neighbor redirect messages, which ultimately reduces link-layer congestion.
Note |
A router must not update its routing tables after receiving a neighbor redirect message, and hosts must not originate neighbor redirect messages. |
This task sets the IP Address Repository Manager (IPARM) address conflict resolution parameters:
Static Policy Resolution
Longest Prefix Address Conflict Resolution
Highest IP Address Conflict Resolution
Route-Tag Support for Connected Routes
The static policy resolution configuration prevents new address configurations from affecting interfaces that are currently running.
Sets the conflict policy to static, that is, prevents new interface addresses from affecting the currently running interface.
Router# configure
Router(config)#ipv4 conflict-policy static
*/For IPv6, use the ipv6 conflict-policy static command/*
Router(config)#commit
Router#show running-config | in ipv4 config
Building configuration...
!! IOS XR Configuration version = 6.0.0.26I
!! Last configuration change at Mon Dec 14 21:57:27 2015 by root
!
hostname sample-83
logging console debugging
username root
group root-lr
group test
secret 5 $1$d2NC$RbAdqdU7kw/eKJpMo/GJI1
!
cdp
ipv4 conflict-policy static
interface Loopback0
ipv4 address 192.0.2.1 255.255.255.0
!
…..
Router#show arm ipv4 conflicts
F Forced down
| Down interface & addr Up interface & addr VRF
F Hu0/0/0/1 192.0.2.1/24 Hu0/0/0/1 192.0.2.27/24 default This conflict resolution policy attempts to give highest precedence to the IP address that has the longest prefix length, that is, all addresses within the conflict-set that do not conflict with the longest prefix address of the currently running interface are allowed to run as well.
Configures longest prefix address conflict resolution.
Router# configure
Router(config)# ipv4 conflict-policy longest-prefix
*/For IPv6, use the ipv6 conflict-policy command*/
Router(config)# commitRouter# show running-config | in longest-prefix
Building configuration...
ipv4 conflict-policy longest-prefixRouter#show arm ipv4 conflicts
F Forced down
| Down interface & addr Up interface & addr VRF
F Hun0/0/0/1 192.0.2.2/24 HundredGigE0/0/0/1 192.0.2.1/24 default
This conflict resolution policy attempts to give highest precedence to the IP address that has the highest value, that is, the IP address with the highest value gets precedence.
Configures highest IP address conflict resolution.
Router# configure
Router(config)#ipv4 conflict-policy highest-ip
*/For IPv6, use the ipv6 conflict-policy highest-ip command/*
Router(config)#commitRouter#show running-config | in highest-ip
Building configuration...
ipv4 conflict-policy highest-ipRouter#show arm ipv4 conflicts
F Forced down
| Down interface & addr Up interface & addr VRF
F Hun0/0/0/1 192.0.2.2/24 HundredGigE0/0/0/1 192.0.2.1/24 default
Forced down interface Up interface VRF
The Route-Tag Support for Connected Routes feature attaches a tag with all IPv4 and IPv6 addresses of an interface. The tag is propagated from the IPv4 and IPv6 management agents (MA) to the IPv4 and IPv6 address repository managers (ARM) to routing protocols, thus enabling the user to control the redistribution of connected routes by looking at the route tags, by using routing policy language (RPL) scripts. This prevents the redistribution of some interfaces, by checking for route tags in a route policy. The route tag feature is already available for static routes and connected routes (interfaces) wherein the route tags are matched to policies and redistribution can be prevented.
Specifies an IPv4 address 192.0.2.27 that has a route tag of 20 to the interface HundredGigE 0/0/0/24.
Router# configure
Router(config)#interface HundredGigE 0/0/0/24
Router(config-if)#ipv4 address 192.0.2.27/24 route-tag 20
Router(config)#commitRouter#show running-config interface HundredGigE 0/0/0/24
interface HundredGigE0/0/0/24
ipv4 address 192.0.2.27 255.255.255.0 route-tag 20
shutdown
!Verify the parameters of the route.
Router#show route 192.0.2.27
Routing entry for 192.0.2.27/24
Known via "local", distance 0, metric 0 (connected)
Tag 20
Routing Descriptor Blocks
directly connected, via HundredGigE0/0/0/24
Route metric is 0
No advertising protos.
IPv4 and IPv6 Address Repository Manager (IPARM) enforces the uniqueness of global IP addresses configured in the system, and provides global IP address information dissemination to processes on route processors (RPs) and line cards (LCs) using the IP address consumer application program interfaces (APIs), which includes unnumbered interface information.
There are two parts to conflict resolution; the conflict database and the conflict set definition.
IPARM maintains a global conflict database. IP addresses that conflict with each other are maintained in lists called conflict sets. These conflict sets make up the global conflict database.
A set of IP addresses are said to be part of a conflict set if at least one prefix in the set conflicts with every other IP address belonging to the same set. For example, the following four addresses are part of a single conflict set.
address 1: 10.1.1.1/16
address 2: 10.2.1.1/16
address 3: 10.3.1.1/16
address 4: 10.4.1.1/8
When a conflicting IP address is added to a conflict set, an algorithm runs through the set to determine the highest precedence address within the set.
This conflict policy algorithm is deterministic, that is, the user can tell which addresses on the interface are enabled or disabled. The address on the interface that is enabled is declared as the highest precedence ip address for that conflict set.
The conflict policy algorithm determines the highest precedence ip address within the set.
|
Feature Name |
Release Information |
Feature Description |
| VRF Fallback and Redirect | Release 7.3.16 |
The VRF fallback functionality of this feature allows you to configure a fallback VRF route which is a better alternative than a default route from the global routing table that requires an explicit next hop. If the destination prefix of a data packet does not have a match in the VRF table, the fallback VRF table is used. The VRF redirect functionality of this feature allows the forwarding of IPv4 and IPv6 packets into a configured next hop VRF. The VRF fallback functionality of this feature allows you to configure a fallback VRF route which is a better alternative than a default route from the global routing table that requires an explicit next hop. If the destination prefix of a data packet does not have a match in the VRF table, the fallback VRF table is used. The VRF redirect functionality of this feature allows the forwarding of IPv4 and IPv6 packets into a configured next hop VRF. |
Virtual Routing and Forwarding (VRF) is an IP technology that allows multiple instances of a routing table to coexist simultaneously on the same router. Because the routing instances are independent, the same IP addresses can be used without conflict.
If the destination prefix of a data packet does not match any route in the configured VRF, a default route is identified from the global routing table. However, using a default route needs an explicit next hop and that may not be efficient. A better option is to configure a fallback VRF route. If the destination does not have a match in the VRF table, the fallback VRF table is used. The fallback VRF can either be the global routing table or a non-global VRF table.
The following restrictions apply if you configure a fallback VRF route:
You can configure only one fallback VRF route for each address family of each primary VRF.
Ping, traceroute, or any slow path application is not supported on fallback VRF because there is no support for LPTS receive trap.
Only 512 VRFs and 1 global table are supported ion the router.
If you configure a static default route to a VRF, the static default route takes precedence over the fallback VRF. If you configure the default route for a VRF, the global routing table is used for a route lookup. The default route is always directed to the configured next hop.
If a route lookup for a packet fails in the primary VRF, the route lookup is retried in the fallback VRF.
If you configure both ACL-based forwarding (ABF) VRF redirect and VRF fallback for a packet, then the packet is recycled twice. Therefore, the routing performance of the packet goes down by up to 33 percent.
If a route for a packet is found in the fallback VRF, only the Glean IPv4 and Glean IPv6 adjacency packets are punted successfully.
In a looped configuration, if the route for a packet is not found in both the primary and fallback VRF, the packet loops in the recycle path. Eventually, the packet is dropped in the recycle egress queue. The recycle queue is of highest priority. Therefore, if there is a high rate of looped traffic, other good recycled packets may be dropped.
Configure VRF Fallback
Configure VRF Redircct
Configure the fallback-vrf command for a destination that does not match any routes in the configured VRF.
Router# configure
Router(config)# vrf vrf1
Router(config-vrf)# fallback-vrf vrf2
Router# show access-list 8075-BYPASS-V4 hardware ingress detail location 0/0/CPU0
Hit Packet Count: 1123
show cef vrf vrf100 192.0.2.1 hardware egress location 0/1/CPU0
0.0.0.0/0, version 0, proxy default, internal 0x1200011 0x0 (ptr 0x8983f534) [1], 0x0 (0x894fa728), 0x0 (0x0)
Updated Mar 21 14:01:43.765
Prefix Len 0, traffic index 0, precedence n/a, priority 15
via 0.0.0.0/32, 0 dependencies, weight 0, class 0 [flags 0x0]
path-idx 0 NHID 0x0 [0x8871b168 0x0]
next hop VRF - 'vrf200', table - 0xe0000008
next hop 0.0.0.0/32
LEAF - HAL pd context :
sub-type : IPV4, ecd_marked:0, has_collapsed_ldi:0
collapse_bwalk_required:0, ecdv2_marked:0,
HW Walk:
You can configure the VRF R edirect using an ACL-based forwarding (ABF).
Router(config)# ipv6 access-list IPV6-BYPASS-ACL
Router(config)# 5 permit ipv6 any any nexthop1 vrf tms-bypass-l3vrf
Router(config)# ipv4 access-list 8075-BYPASS-V4
Router(config)# 10 permit ipv4 any any nexthop1 vrf tms-bypass-l3vrf
/* You can configure either a HundredGig or a bundle interface. */
Router(config)# interface HundredGigE0/0/0/1
Router(config-if)# ipv4 address 103.4.96.1 255.255.255.254
Router(config-if)# ipv6 address 2620:0:1cff:dead:beee::1/127
Router(config-if)# ipv4 access-group 8075-BYPASS-V4 ingress
Router(config-if)# ipv6 access-group IPV6-BYPASS-ACL ingress
ipv6 access-list IPV6-BYPASS-ACL
5 permit ipv6 any any nexthop1 vrf tms-bypass-l3vrf
!
ipv4 access-list 8075-BYPASS-V4
10 permit ipv4 any any nexthop1 vrf tms-bypass-l3vrf
!
interface HundredGigE0/0/0/1 (or bundle interface)
ipv4 address 103.4.96.1 255.255.255.254
ipv6 address 2620:0:1cff:dead:beee::1/127
ipv4 access-group 8075-BYPASS-V4 ingress
ipv6 access-group IPV6-BYPASS-ACL ingress
Verify VRF redirect.
show route vrf tms-bypass-l3vrf
S* 0.0.0.0/0 [1/0] via 0.0.0.0 (nexthop in vrf tms-l3vrf), 00:15:48
B 99.99.99.0/24 [20/2219] via 29.55.0.1 (nexthop in vrf default), 00:08:30
show access-list 8075-BYPASS-V4 hardware ingress detail location 0/0/CPU0
Hit Packet Count: 1123
|
Feature Name |
Release Information |
Feature Description |
| Local Station MAC Address for Router | Release 7.9.1 |
Local Station MAC Address is the MAC address for the router that applies to all interfaces, including VRFs. You can configure Local Station MAC Address for a router using the hw-module local-station-mac command. This feature allows the router and its interfaces to have one network-wide identity and helps in identifying the neighboring devices in the network while using static ARP. The feature introduces these changes:
|
When the router receives a Layer 3 traffic packet, the destination MAC address in it would be the MAC address of the interface in the router that accepted the traffic packet. In dynamic ARP, the router learns such MAC address while exchanging ARP response packets. But, when using static ARP, the router needs to support a system-wide MAC address to identify the router. This system-wide MAC address should be available in the static ARP table of the router. Previously, the router had the MAC address of each interface in the static ARP table. Here, the static ARP entries utilize higher resources on the router as it needs to maintain a pool of static ARP entries for all the interfaces against the current implementation with one single entry per system.
The Cisco Silicon One Q100 ASICs don’t support Local Station MAC Address for the Router. For a list of Cisco 8000 Series hardware using Cisco Silicon One Q100 ASIC, refer Cisco 8000 Series Routers Data Sheet.
The following section details on configuring the Local Station MAC address for a router:
Configuration
Router# config
Router(config)# hw-module local-station-mac B03F.C98C.B948
Router(config)# commitRunning Configuration
Router# show running-config hw-module local-station-mac
hw-module local-station-mac B03F.C98C.B948
! Verification
Router# show hw-module local-station-mac
--------------------------------------------------------------
Knob Status Applied Action
--------------------------------------------------------------
Local-Station-MAC Configured Yes None
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