Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for
Configuring IP Multicast Routing
The following are the prerequisites for configuring IP multicast
routing:
To use the IP
multicast routing feature on the
switch, the
switch or active
switch must be running the IP Services
feature set.
You must enable
IP multicast routing and configure the PIM version and PIM mode on the
switch. After performing these tasks, the
switch can then forward multicast packets and
can populate its multicast routing table.
To participate
in IP multicasting, the multicast hosts, routers, and multilayer
switch must have IGMP operating.
Restrictions for
Configuring IP Multicast Routing
The
following are the restrictions for configuring IP multicast routing:
IP multicast
routing is not supported on
switches running the LAN Base feature set.
Layer 3 IPv6
multicast routing is not supported on the
switch.
High-availability support for Layer 3 multicast routing is not
supported.
You cannot have a
switch stack containing a mix of Catalyst
3850 and Catalyst 3650
switches.
Information About IP Multicast Routing
IP multicasting is an efficient way to use network resources, especially for bandwidth-intensive services such as audio and video. IP multicast routing enables a host (source) to send packets to a group of hosts (receivers) anywhere within the IP network by using a special form of IP address called the IP multicast group address.
The sending host inserts the multicast group address into the IP destination address field of the packet, and IP multicast routers and multilayer switches forward incoming IP multicast packets out all interfaces that lead to members of the multicast group. Any host, regardless of whether it is a member of a group, can send to a group. However, only the members of a group receive the message.
Note
For complete syntax and usage information for the commands used in this chapter, see the IP Multicast Command Reference, Cisco IOS XE Release 3SE (Catalyst 3850 Switches).
For information on configuring the Multicast Source Discovery Protocol (MSDP), see the Catalyst 3850 Routing Configuration Guide.
Cisco IOS software supports the following protocols to implement IP multicast routing:
Internet Group Management Protocol (IGMP) is used among hosts on a LAN and the routers (and multilayer switches) on that LAN to track the multicast groups of which hosts are members.
Protocol-Independent Multicast (PIM) protocol is used among routers and multilayer switches to track which multicast packets to forward to each other and to their directly connected LANs.
Note
The switch does not support the Distance Vector Multicast Routing Protocol (DVMRP) nor the Cisco Group Management Protocol (CGMP).
Figure 1. IP Multicast Routing Protocols. The following figure shows where the Cisco-supported protocols for the switch operate within the IP multicast environment.
According to IPv4 multicast standards, the MAC destination multicast address begins with 0100:5e and is appended by the last 23 bits of the IP address. For example, if the IP destination address is 239.1.1.39, the MAC destination address is 0100:5e01:0127.
A multicast packet is unmatched when the destination IPv4 address does not match the destination MAC address. The switch forwards the unmatched packet in hardware based upon the MAC address table. If the destination MAC address is not in the MAC address table, the switch floods the packet to the all port in the same VLAN as the receiving port.
The switch uses the Multicast Forwarding Information Base (MFIB) architecture and the Multicast Routing Information Base (MRIB) for IP multicast.
The MFIB architecture
provides both modularity and separation between the multicast control
plane (Protocol Independent Multicast [PIM] and Internet Group
Management Protocol [IGMP]) and the multicast forwarding plane
(MFIB). This architecture is used in Cisco IOS IPv6 multicast
implementations.
MFIB itself is a multicast routing protocol independent forwarding
engine; that is, it does not depend on PIM or any other multicast
routing protocol. It is responsible for:
Forwarding multicast packets
Registering with the MRIB to learn the entry and interface flags set by the control plane
Handling data-driven events that must be sent to the control plane
Maintaining counts, rates, and bytes of received, dropped, and forwarded multicast packets
The MRIB is the communication channel between MRIB clients.
Examples of MRIB clients are PIM, IGMP, the multicast routing
(mroute) table, and the MFIB.
Multicast is based on the concept of a group. An arbitrary group of
receivers expresses an interest in receiving a particular data
stream. This group does not have any physical or geographical
boundaries. The hosts can be located anywhere on the Internet. Hosts
that are interested in receiving data flowing to a particular group
must join the group using IGMP. Hosts must be a member of the group
to receive the data stream.
Administratively-scoped boundaries can be used to limit the forwarding of multicast traffic outside of a domain or subdomain. This approach uses a special range of multicast addresses, called administratively-scoped addresses, as the boundary mechanism. If you configure an administratively-scoped boundary on a routed interface, multicast traffic whose multicast group addresses fall in this range cannot enter or exit this interface, which provides a firewall for multicast traffic in this address range.
Note
Multicast boundaries and TTL thresholds control the scoping of multicast domains; however, TTL thresholds are not supported by the switch. You should use multicast boundaries instead of TTL thresholds to limit the forwarding of multicast traffic outside of a domain or a subdomain.
Figure 2. Administratively-Scoped Boundaries. The following figure shows that Company XYZ has an administratively-scoped boundary set for the multicast address range 239.0.0.0/8 on all routed interfaces at the perimeter of its network. This boundary prevents any multicast traffic in the range 239.0.0.0 through 239.255.255.255 from entering or leaving the network. Similarly, the engineering and marketing departments have an administratively-scoped boundary of 239.128.0.0/16 around the perimeter of their networks. This boundary prevents multicast traffic in the range of 239.128.0.0 through 239.128.255.255 from entering or leaving their respective networks.
You can define an administratively-scoped boundary on a routed interface for multicast group addresses. A standard access list defines the range of addresses affected. When a boundary is defined, no multicast data packets are allowed to flow across the boundary from either direction. The boundary allows the same multicast group address to be reused in different administrative domains.
The IANA has designated the multicast address range 239.0.0.0 to 239.255.255.255 as the administratively-scoped addresses. This range of addresses can then be reused in domains administered by different organizations. The addresses would be considered local, not globally unique.
For all multicast routing
protocols, the entire stack appears as a single router to the network and
operates as a single multicast router.
In a
switch stack, the active
switch
performs these functions:
It is responsible for
completing the IP multicast routing functions of the stack. It fully
initializes and runs the IP multicast routing protocols.
It builds and maintains the
multicast routing table for the entire stack.
It is responsible for
distributing the multicast routing table to all stack members.
The
stack members perform these functions:
They act as multicast routing
standby devices and are ready to take over if there is a active
switch
failure.
If the active
switch
fails, all stack members delete their multicast routing tables. The newly
elected active
switch
starts building the routing tables and distributes them to the stack members.
They do not build multicast
routing tables. Instead, they use the multicast routing table that is
distributed by the active
switch.
Default Multicast Routing Configuration
This table describes the default multicast routing configuration for the switch.
You must enable IP multicast
routing and configure the PIM version and mode. After performing these tasks,
the software can then forward multicast packets, and the
switch can populate its multicast routing
table.
You can configure an
interface to be in PIM dense mode, sparse mode, or sparse-dense mode. The
switch populates its multicast routing
table and forwards multicast packets it receives from its directly connected
LANs according to the mode setting. You must enable PIM in one of these modes
for an interface to perform IP multicast routing.
Enabling PIM on an interface also enables IGMP operation on that
interface.
Note
If you enable PIM on multiple
interfaces, when most of these interfaces are not on the outgoing interface
list, and IGMP snooping is disabled, the outgoing interface might not be able
to sustain line rate for multicast traffic because of the extra replication.
In populating the multicast
routing table, dense-mode interfaces are always added to the table. Sparse-mode
interfaces are added to the table only when periodic join messages are received
from downstream devices or when there is a directly connected member on the
interface.
When forwarding from a LAN, sparse-mode operation occurs if
there is a rendezvous point (RP) known for the group. An RP acts as the meeting
place for sources and receivers of multicast data. If an RP exists, the packets
are encapsulated and sent toward the RP. When no RP is known, the packet is
flooded in a dense-mode fashion. If the multicast traffic from a specific
source is sufficient, the receiver’s first-hop router might send join messages
toward the source to build a source-based distribution tree.
By default, multicast routing
is disabled, and there is no default mode setting.
IP multicast
routing is supported with Multicast Forwarding Information Base (MFIB) and
Multicast Routing Information Base (MRIB).
Step 4
interfaceinterface-id
Example:
Switch(config)# interface
gigabitethernet 1/0/1
Specifies the Layer 3
interface on which you want to enable multicast routing, and enters interface
configuration mode.
The specified interface
must be one of the following:
A routed port—A physical
port that has been configured as a Layer 3 port by entering the
no switchport
interface configuration command. You will also need to enable IP PIM
sparse-dense-mode on the interface, and join the interface as a statically
connected member to an IGMP static group. For a configuration example, see
Example: Interface Configuration as a Routed Port
An SVI—A VLAN interface
created by using the
interface vlanvlan-id
global configuration command. You will also need to enable IP PIM
sparse-dense-mode on the VLAN, join the VLAN as a statically connected member
to an IGMP static group, and then enable IGMP snooping on the VLAN, the IGMP
static group, and physical interface. For a configuration example, see
Example: Interface Configuration as an SVI
These interfaces
must have IP addresses assigned to them.
Step 5
ip pim {dense-mode |
sparse-mode |
sparse-dense-mode}
Example:
Switch(config-if)# ip pim
sparse-dense-mode
Enables a PIM mode on the interface.
By default, no
mode is configured.
The keywords have
these meanings:
dense-mode—Enables dense mode of operation.
sparse-mode—Enables sparse mode of operation. If
you configure sparse mode, you must also configure an RP.
sparse-dense-mode—Causes the interface to be
treated in the mode in which the group belongs. Sparse-dense mode is the
recommended setting.
You can use the
following procedure to configure IPv4 Multicast Forwarding Information Base
(MFIB) interrupt-level IP multicast forwarding of incoming packets or outgoing
packets on the
switch.
Note
After you have
enabled IP multicast routing by using the
ip
multicast-routing command, IPv4 multicast forwarding is enabled.
Because IPv4 multicast forwarding is enabled by default, you can use the
no form of the
ip mfib command
to disable IPv4 multicast forwarding.
SUMMARY STEPS
1.enable
2.configureterminal
3.ip mfib
4.exit
5.show
running-config
6.copy
running-config startup-config
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Switch> enable
Enables
privileged EXEC mode.
Enter your password if
prompted.
Step 2
configureterminal
Example:
Switch# configure terminal
Enters the global configuration mode.
Step 3
ip mfib
Example:
Switch(config)# ip mfib
Enables IP
multicast forwarding.
Step 4
exit
Example:
Switch(config)# exit
Returns to
privileged EXEC mode.
Step 5
show
running-config
Example:
Switch# show running-config
Verifies your
entries.
Step 6
copy
running-config startup-config
Example:
Switch# copy running-config
startup-config
(Optional) Saves
your entries in the configuration file.
Configuring a Static
Multicast Route (mroute) (CLI)
You
can use the following procedure to configure static mroutes. Static mroutes are
similar to unicast static routes but differ in the following ways:
Static mroutes
are used to calculate RPF information, not to forward traffic.
Static mroutes
cannot be redistributed.
Static
mroutes are strictly local to the
switch on which they are defined. Because
Protocol Independent Multicast (PIM) does not have its own routing protocol,
there is no mechanism to distribute static mroutes throughout the network.
Consequently, the administration of static mroutes tends to be more complicated
than the administration of unicast static routes.
When static mroutes
are configured, they are stored on the
switch in a separate table referred to as
the static mroute table. When configured, the ip mroute command enters a static mroute into the
static mroute table for the source address or source address range specified
for the source-address and mask arguments. Sources that match the source
address or that fall in the source address range specified for the
source-address argument will RPF to either the interface associated with the IP
address specified for the
rpf-address
argument or the local interface on the
switch specified for the
interface-type
and
interface-number arguments. If an IP address is specified
for the
rpf-address
argument, a recursive lookup is done from the unicast routing table on this
address to find the directly connected neighbor.
If there are
multiple static mroutes configured, the
switch performs a longest-match lookup of
the mroute table. When the mroute with the longest match (of the
source-address) is found, the search terminates and the information in the
matching static mroute is used. The order in which the static mroutes are
configured is not important.
The administrative
distance of an mroute may be specified for the optional distance argument. If a
value is not specified for the distance argument, the distance of the mroute
defaults to zero. If the static mroute has the same distance as another RPF
source, the static mroute will take precedence. There are only two exceptions
to this rule: directly connected routes and the default unicast route.
Switch(configure)# ip mroute 10.1.1.1 255.255.255.255 10.2.2.2
The source IP
address 10.1.1.1 is configured to be reachable through the interface associated
with IP address 10.2.2.2.
Step 4
exit
Example:
Switch(config)# exit
Returns to
privileged EXEC mode.
Step 5
show
running-config
Example:
Switch# show running-config
(Optional)
Verifies your entries.
Step 6
copy
running-config startup-config
Example:
Switch# copy running-config
startup-config
(Optional) Saves
your entries in the configuration file.
Configuring sdr Listener Support
The MBONE is the small subset of Internet routers and hosts that are interconnected and capable of forwarding IP multicast traffic. Other multimedia content is often broadcast over the MBONE. Before you can join a multimedia session, you need to know what multicast group address and port are being used for the session, when the session is going to be active, and what sort of applications (audio, video, and so forth) are required on your workstation. The MBONE Session Directory Version 2 (sdr) tool provides this information. This freeware application can be downloaded from several sites on the World Wide Web, one of which is http://www.video.ja.net/mice/index.html.
SDR is a multicast application that listens to a well-known multicast group address and port for Session Announcement Protocol (SAP) multicast packets from SAP clients, which announce their conference sessions. These SAP packets contain a session description, the time the session is active, its IP multicast group addresses, media format, contact person, and other information about the advertised multimedia session. The information in the SAP packet is displayed in the SDR Session Announcement window.
By default, the
switch does not listen to session directory
advertisements.
This procedure is optional.
SUMMARY STEPS
1.enable
2.configureterminal
3.interfaceinterface-id
4.ip sap
listen
5.end
6.show
running-config
7.copy
running-config startup-config
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Switch> enable
Enables
privileged EXEC mode.
Enter your password if
prompted.
Step 2
configureterminal
Example:
Switch# configure terminal
Enters the global configuration mode.
Step 3
interfaceinterface-id
Example:
Switch(config)# interface
gigabitethernet 1/0/1
Specifies the
interface to be enabled for sdr, and enters interface configuration mode.
The specified interface must be one of the following:
A routed port—A physical port
that has been configured as a Layer 3 port by entering the
no switchport
interface configuration command. You will also need to enable IP PIM
sparse-dense-mode on the interface, and join the interface as a statically
connected member to an IGMP static group. For a configuration example, see
Example: Interface Configuration as a Routed Port
An SVI—A VLAN interface
created by using the
interface vlanvlan-id global
configuration command. You will also need to enable IP PIM sparse-dense-mode on
the VLAN, join the VLAN as a statically connected member to an IGMP static
group, and then enable IGMP snooping on the VLAN, the IGMP static group, and
physical interface. For a configuration example, see
Example: Interface Configuration as an SVI
These interfaces must have IP
addresses assigned to them.
Step 4
ip sap
listen
Example:
Switch(config-if)# ip sap listen
Enables the
switch software to listen to session
directory announcements.
Step 5
end
Example:
Switch(config-if)# end
Returns to
privileged EXEC mode.
Step 6
show
running-config
Example:
Switch# show running-config
Verifies your
entries.
Step 7
copy
running-config startup-config
Example:
Switch# copy running-config
startup-config
(Optional) Saves
your entries in the configuration file.
Limiting How Long an sdr Cache Entry Exists
(CLI)
By default, entries are never
deleted from the sdr cache. You can limit how long the entry remains active so
that if a source stops advertising SAP information, old advertisements are not
unnecessarily kept.
This procedure is optional.
SUMMARY STEPS
1.enable
2.configureterminal
3.ip sap
cache-timeoutminutes
4.end
5.show
running-config
6.show ip
sap
7.copy
running-config startup-config
DETAILED STEPS
Command or Action
Purpose
Step 1
enable
Example:
Switch> enable
Enables
privileged EXEC mode.
Enter your password if
prompted.
Step 2
configureterminal
Example:
Switch# configure terminal
Enters the global configuration mode.
Step 3
ip sap
cache-timeoutminutes
Example:
Switch(config)# ip sap cache-timeout 30
Limits how long a
Session Announcement Protocol (SAP) cache entry stays active in the cache.
By default,
entries are never deleted from the cache.
For
minutes, the range is 1 to 1440 minutes (24
hours).
Step 4
end
Example:
Switch(config)# end
Returns to privileged EXEC mode.
Step 5
show
running-config
Example:
Switch# show running-config
Verifies your
entries.
Step 6
show ip
sap
Example:
Switch# show ip sap
Displays the SAP
cache.
Step 7
copy
running-config startup-config
Example:
Switch# copy running-config
startup-config
(Optional) Saves
your entries in the configuration file.
Creates a
standard access list, repeating the command as many times as necessary.
For
access-list-number, the ranges are as follows:
access-list-number 1—99 (IP standard access list)
access-list-number 100—199 ( IP extended access list)
access-list-number 1300—1999 (IP standard access list - expanded
range)
access-list-number 2000—2699 (IP extended access list - expanded
range)
The
dynamic-extended keyword extends the dynamic ACL
absolute timer.
The
rate-limit keyword permits a simple rate-limit
specific access list.
The access list
is always terminated by an implicit deny statement for everything.
Step 4
interfaceinterface-id
Example:
Switch(config)# interface gigabitEthernet1/0/1
Specifies the
interface to be configured, and enters interface configuration mode.
The specified interface
must be one of the following:
A routed port—A physical
port that has been configured as a Layer 3 port by entering the
no switchport
interface configuration command. You will also need to enable IP PIM
sparse-dense-mode on the interface, and join the interface as a statically
connected member to an IGMP static group. For a configuration example, see
Example: Interface Configuration as a Routed Port
An SVI—A VLAN interface
created by using the
interface vlanvlan-id
global configuration command. You will also need to enable IP PIM
sparse-dense-mode on the VLAN, join the VLAN as a statically connected member
to an IGMP static group, and then enable IGMP snooping on the VLAN, the IGMP
static group, and physical interface. For a configuration example, see
Example: Interface Configuration as an SVI
These interfaces
must have IP addresses assigned to them.
Step 5
ip multicast
boundaryaccess-list-number
Example:
Switch(config-if)# ip multicast boundary 99
Configures the
boundary, specifying the access list you created in Step 2.
Additional
command options include:
For
access-list-number, the ranges are as follows:
access-list-number 1—99 (IP standard access list)
access-list-number 100—199 ( IP extended access list)
access-list-number 1300—1999 (IP standard access list - expanded
range)
access-list-number 2000—2699 (IP extended access list - expanded
range)
Word—IP named access list.
filter-autorp—Filter AutoRP packet contents.
in—Restrict (s,g) creation when this interface is
the RPF.
out—Restrict interface addition to outgoing list.
Step 6
end
Example:
Switch(config-if)# end
Returns to
privileged EXEC mode.
Step 7
show
running-config
Example:
Switch# show running-config
Verifies your
entries.
Step 8
copy
running-config startup-config
Example:
Switch# copy running-config
startup-config
(Optional)
Saves your entries in the configuration file.
What to Do Next
Proceed to the
other supported IP multicast routing procedures.
You can remove all contents of a particular cache, table, or database. Clearing a cache, table, or database might be necessary when the contents of the particular structure are or suspected to be invalid.
You can use any of the privileged EXEC commands in the following table to clear IP multicast caches, tables, and databases.
Table 2 Commands for Clearing Caches, Tables, and Databases
Command
Purpose
clear ip igmp group {group [ hostname | IP address] | vrfnamegroup [ hostname | IP address] }
Deletes entries from the IGMP cache.
clear ip mfib { counters [group | source] | global counters [group | source] | vrf * }
Clears all active IPv4 Multicast Forwarding Information Base
(MFIB) traffic counters.
clear ip mrm {status-report [ source ] }
IP multicast routing clear commands.
clear ip mroute { * | [hostname | IP address] | vrfnamegroup [ hostname | IP address] }
Deletes entries from the IP multicast routing table.
Clears the Multicast Source Discovery Protocol (MSDP) cache.
clear ip multicast { limit | redundancy statistics }
Clears the IP multicast information.
clear ip pim { df [ int | rprp address ] | interface | rp-mapping [rp address] | vrfvpn name { df | interface | rp-mapping }
Clears the PIM cache.
clear ip sap [group-address | “session-name”]
Deletes the Session Directory Protocol Version 2 cache or an sdr cache entry.
Displaying System and Network Statistics
You can display specific statistics, such as the contents of IP routing tables, caches, and databases.
Note
This release does not support per-route statistics.
You can display information to learn resource usage and solve network problems. You can also display information about node reachability and discover the routing path that packets of your device are taking through the network.
You can use any of the privileged EXEC commands in the following table to display various routing statistics.
Table 3 Commands for Displaying System and Network Statistics
Command
Purpose
ping [group-name | group-address]
Sends an ICMP Echo Request to a multicast group address.
show ip igmp filter
Displays IGMP filter information.
show ip igmp groups [type-number | detail ]
Displays the multicast groups that are directly connected to the switch and that were learned through IGMP.
show ip igmp interface [type number]
Displays multicast-related information about an interface.
show ip igmp membership [ name/group address | all | tracked ]
Displays IGMP membership information for forwarding.
show ip igmp profile [ profile_number]
Displays IGMP profile information.
show ip igmp ssm-mapping [ hostname/IP address ]
Displays IGMP SSM mapping information.
show ip igmp static-group {class-map [ interface [ type ] ]
Displays static group information.
show ip igmp vrf
Displays the selected VPN Routing/Forwarding instance by name.
show ip mfib [ type number ]
Displays the IP multicast forwarding information base.
show ip mrib { client | route | vrf }
Displays the multicast routing information base.
show ip mrm { interface | manager | status-report }
Displays the IP multicast routing monitor information.
show ip mroute [group-name | group-address] [source] [ count | interface | proxy | pruned | summary | verbose]
Displays the contents of the IP multicast routing table.
show ip msdp { count | peer | rpf-peer | sa-cache | summary | vrf }
Displays the Multicast Source Discovery Protocol (MSDP) information.
show ip multicast [ interface | limit | mpls | redundancy | vrf ]
Displays global multicast information.
show ip pim interface [type number] [count | detail | df | stats ]
Displays information about interfaces configured for PIM. This command is available in all software images.
show ip pim all-vrfs { tunnel }
Display all VRFs.
show ip pim autorp
Display global auto-RP information.
show ip pim boundary [ type number ]
Displays boundary information.
show ip pim bsr-router
Display bootstrap router information (version 2).
show ip pim interface [ type number ]
Displays PIM interface information.
show ip pim mdt [ bgp ]
Displays multicast tunnel information.
show ip pim neighbor [type number]
Lists the PIM neighbors discovered by the switch. This command is available in all software images.
show ip pim rp [group-name | group-address]
Displays the RP routers associated with a sparse-mode multicast group. This command is available in all software images.
show ip pim rp-hash [group-name | group-address]
Displays the RP to be chosen based upon the group selected.
show ip pim tunnel [ tunnel | verbose ]
Displays the registered tunnels.
show ip pim vrfname
Displays VPN routing and forwarding instances.
show ip rpf {source-address | name}
Displays how the switch is doing Reverse-Path Forwarding (that is, from the unicast routing table, DVMRP routing table, or static mroutes).
Command parameters include:
Host name or IP address—IP name or group address.
Select—Group-based VRF select information.
vrf—Selects VPN Routing/Forwarding instance.
show ip sap [group | “session-name” | detail]
Displays the Session Announcement Protocol (SAP) Version 2 cache.
Command parameters include:
A.B.C.D—IP group address.
WORD—Session name (in double quotes).
detail—Session details.
Monitoring IP Multicast Routing
You can use the privileged EXEC commands in the following table to monitor IP multicast routers, packets, and paths.
Table 4 Commands for Monitoring IP Multicast Routing
Command
Purpose
mrinfo { [hostname | address] | vrf}
Queries a multicast router or multilayer switch about which neighboring multicast devices are peering with it.
mstat { [hostname | address] | vrf}
Displays IP multicast packet rate and loss information.
mtrace { [hostname | address] | vrf}
Traces the path from a source to a destination branch for a multicast distribution tree for a given group.
The software answers mrinfo requests sent by mrouted systems and Cisco routers and multilayer switches. The software returns information about neighbors through DVMRP tunnels and all the routed interfaces. This information includes the metric (always set to 1), the configured TTL threshold, the status of the interface, and various flags. You can also use the mrinfo privileged EXEC command to query the router or switch itself, as in this example:
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