The Enhanced Interior
Gateway Routing Protocol (EIGRP) is an enhanced version of IGRP developed by
Cisco. This module describes the concepts and tasks you need to implement basic
EIGRP configuration using Cisco IOS XR software. EIGRP uses distance vector
routing technology, which specifies that a router need not know all the router
and link relationships for the entire network. Each router advertises
destinations with a corresponding distance and upon receiving routes, adjusts
the distance and propagates the information to neighboring routes.
For EIGRP configuration
information related to the following features, see the
Related Documents section of this module.
For more information
about EIGRP on the Cisco IOS XR software and complete descriptions of the EIGRP
commands listed in this module, see the
Commands chapter in the
Routing Command Reference for Cisco ASR 9000 Series Routers. To
locate documentation for other commands that might appear while executing a
configuration task, search online in the
Cisco IOS XR software
master command index.
for Implementing EIGRP
feature was introduced.
Metric Support feature was added
for Site of origin (SoO) attribute was added
Prerequisites for Implementing EIGRP
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.
restrictions are employed when running EIGRP on this version of
Cisco IOS XR software:
A maximum of 4 instances of
an EIGRP process is supported.
allowed for EIGRP process name are
@ . # : - _
Management Protocol (SNMP) MIB is not supported.
routes are not automatically redistributed into EIGRP, because there are no
configuration (either through the
default-metric command or a route policy) is required
for redistribution of connected and static routes.
Auto summary is
disabled by default.
Stub leak maps are
Information About Implementing EIGRP
To implement EIGRP, you need to understand the following concepts:
EIGRP Functional Overview
Enhanced Interior Gateway Routing Protocol (EIGRP) is an interior gateway protocol suited for many different topologies and
media. EIGRP scales well and provides extremely quick convergence times with minimal network traffic.
EIGRP has very low usage of network resources during normal operation. Only hello packets are transmitted on a stable network.
When a change in topology occurs, only the routing table changes are propagated and not the entire routing table. Propagation
reduces the amount of load the routing protocol itself places on the network. EIGRP also provides rapid convergence times
for changes in the network topology.
The distance information in EIGRP is represented as a composite of available bandwidth, delay, load utilization, and link
reliability with improved convergence properties and operating efficiency. The fine-tuning of link characteristics achieves
The convergence technology that EIGRP uses is based on research conducted at SRI International and employs an algorithm referred
to as the Diffusing Update Algorithm (DUAL). This algorithm guarantees loop-free operation at every instant throughout a route
computation and allows all devices involved in a topology change to synchronize at the same time. Routers that are not affected
by topology changes are not involved in recomputations. The convergence time with DUAL rivals that of any other existing routing
EIGRP offers the
convergence—The DUAL algorithm allows routing information to converge as
quickly as any currently available routing protocol.
updates—EIGRP sends incremental updates when the state of a destination
changes, instead of sending the entire contents of the routing table. This
feature minimizes the bandwidth required for EIGRP packets.
mechanism—This is a simple hello mechanism used to learn about neighboring
routers. It is protocol independent.
subnet masks (VLSMs).
scales to large networks.
The following key
features are supported in the
Cisco IOS XR implementation:
(PE)-Customer Edge (CE) protocol support with Site of Origin (SoO) and Border
Gateway Protocol (BGP) cost community support.
support for MPLS.
EIGRP has the
following four basic components:
or neighbor recovery
DUAL finite state
Neighbor discovery or
neighbor recovery is the process that routers use to dynamically learn of other
routers on their directly attached networks. Routers must also discover when
their neighbors become unreachable or inoperative. Neighbor discovery or
neighbor recovery is achieved with low overhead by periodically sending small
hello packets. As long as hello packets are received, the
Cisco IOS XR software can determine that a neighbor is alive
and functioning. After this status is determined, the neighboring routers can
exchange routing information.
The reliable transport
protocol is responsible for guaranteed, ordered delivery of EIGRP packets to
intermixed transmission of multicast and unicast packets.
Some EIGRP packets must be sent reliably and others need not be. For
efficiency, reliability is provided only when necessary.
example, on a multiaccess network that has multicast capabilities (such as
Ethernet) it is not necessary to send hello packets reliably to all neighbors
individually. Therefore, EIGRP sends a single multicast hello with an
indication in the packet informing the receivers that the packet need not be
acknowledged. Other types of packets (such as updates) require acknowledgment,
which is indicated in the packet. The reliable transport has a provision to
send multicast packets quickly when unacknowledged packets are pending. This
provision helps to ensure that convergence time remains low in the presence of
various speed links.
The DUAL finite state
machine embodies the decision process for all route computations. It tracks all
routes advertised by all neighbors. DUAL uses the distance information (known
as a metric) to select efficient, loop-free paths. DUAL selects routes to be
inserted into a routing table based on a calculation of the feasibility
condition. A successor is a neighboring router used for packet forwarding that
has a least-cost path to a destination that is guaranteed not to be part of a
routing loop. When there are no feasible successors but there are neighbors
advertising the destination, a recomputation must occur. This is the process
whereby a new successor is determined. The amount of time required to recompute
the route affects the convergence time. Recomputation is processor intensive;
it is advantageous to avoid unneeded recomputation. When a topology change
occurs, DUAL tests for feasible successors. If there are feasible successors,
it uses any it finds to avoid unnecessary recomputation.
modules are responsible for network layer protocol-specific tasks. An example
is the EIGRP module, which is responsible for sending and receiving EIGRP
packets that are encapsulated in IP. It is also responsible for parsing EIGRP
packets and informing DUAL of the new information received. EIGRP asks DUAL to
make routing decisions, but the results are stored in the IP routing table.
EIGRP is also responsible for redistributing routes learned by other IP routing
EIGRP Configuration Grouping
Cisco IOS XR software groups all EIGRP configuration under router EIGRP configuration mode, including interface configuration portions associated
with EIGRP. To display EIGRP configuration in its entirety, use the show running-config router eigrp command. The command output displays the running configuration for the configured EIGRP instance, including the interface
assignments and interface attributes.
The following examples
show how to enter each of the configuration modes. From a mode, you can enter
command to display the commands available in that mode.
example shows how to enter router configuration mode:
EIGRP interfaces can be configured as either of the following types:
Active—Advertises connected prefixes and forms adjacencies. This is the default type for interfaces.
Passive—Advertises connected prefixes but does not form adjacencies. The passive command is used to configure interfaces as passive. Passive interfaces should be used sparingly for important prefixes, such
as loopback addresses, that need to be injected into the EIGRP domain. If many connected prefixes need to be advertised, then
the redistribution of connected routes with the appropriate policy should be used instead.
an EIGRP Process
Routes from other
protocols can be redistributed into EIGRP. A route policy can be configured
along with the
redistribute command. A metric is required, configured
either through the
default-metric command or under the route policy
configured with the
redistribute command to import routes into EIGRP.
A route policy allows
the filtering of routes based on attributes such as the destination,
origination protocol, route type, route tag, and so on.
redistribution is configured under a VRF, EIGRP retrieves extended communities
attached to the route in the routing information base (RIB). The SoO is used to
filter out routing loops in the presence of MPSL VPN backdoor links.
Metric Weights for EIGRP Routing
EIGRP uses the minimum bandwidth on the path to a destination network and the total delay to compute routing metrics. You
can use the metric weights command to adjust the default behavior of EIGRP routing and metric computations. For example, this adjustment allows you
to tune system behavior to allow for satellite transmission. EIGRP metric defaults have been carefully selected to provide
optimal performance in most networks.
By default, the EIGRP composite metric is a 32-bit quantity that is a sum of the segment delays and lowest segment bandwidth
(scaled and inverted) for a given route. For a network of homogeneous media, this metric reduces to a hop count. For a network
of mixed media (FDDI, Ethernet, and serial lines running from 9600 bits per second to T1 rates), the route with the lowest
metric reflects the most desirable path to a destination.
Mismatched K Values
Mismatched K values (EIGRP metrics) can prevent neighbor relationships from being established and can negatively impact network
convergence. The following example explains this behavior between two EIGRP peers (ROUTER-A and ROUTER-B).
The following error message is displayed in the console of ROUTER-B because the K values are mismatched:
RP/0/RSP0/CPU0:Mar 13 08:19:55:eigrp:%ROUTING-EIGRP-5-NBRCHANGE:IP-EIGRP(0) 1:Neighbor 184.108.40.206 (GigabitEthernet0/6/0/0) is down: K-value mismatch
Two scenarios occur in which this error message can be displayed:
The two routers are connected on the same link and configured to establish a neighbor relationship. However, each router is
configured with different K values.
The following configuration is applied to ROUTER-A. The K values are changed with the metric weights command. A value of 2 is entered for the k1 argument to adjust the bandwidth calculation. The value of 1 is entered for the k3 argument to adjust the delay calculation.
The bandwidth calculation is set to 2 on ROUTER-A and set to 1 (by default) on ROUTER-B. This configuration prevents these
peers from forming a neighbor relationship.
The K-value mismatch error message can also be displayed if one of the two peers has transmitted a “goodbye” message and the
receiving router does not support this message. In this case, the receiving router interprets this message as a K-value mismatch.
The goodbye message is a feature designed to improve EIGRP network convergence. The goodbye message is broadcast when an EIGRP
routing process is shut down to inform adjacent peers about the impending topology change. This feature allows supporting
EIGRP peers to synchronize and recalculate neighbor relationships more efficiently than would occur if the peers discovered
the topology change after the hold timer expired.
The following message is displayed by routers that run a supported release when a goodbye message is received:
RP/0/RSP0/CPU0:Mar 13 09:13:17:eigrp:%ROUTING-EIGRP-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.0.0.20 (GigabitEthernet0/6/0/0) is down: Interface Goodbye received
A Cisco router that runs a software release that does not support the goodbye message can misinterpret the message as a K-value
mismatch and display the following message:
The receipt of a goodbye message by a nonsupporting peer does not disrupt normal network operation. The nonsupporting peer
terminates the session when the hold timer expires. The sending and receiving routers reconverge normally after the sender
Percentage of Link Bandwidth Used for EIGRP Packets
By default, EIGRP packets consume a maximum of 50 percent of the link bandwidth, as configured with the bandwidth interface configuration command. You might want to change that value if a different level of link utilization is required
or if the configured bandwidth does not match the actual link bandwidth (it may have been configured to influence route metric
Floating Summary Routes for an EIGRP Process
You can also use a floating summary route when configuring the summary-address command. The floating summary route is created by applying a default route and administrative distance at the interface level.
The following scenario illustrates the behavior of this enhancement.
shows a network with three routers, Router-A, Router-B, and Router-C. Router-A learns a default route from elsewhere in the
network and then advertises this route to Router-B. Router-B is configured so that only a default summary route is advertised
to Router-C. The default summary route is applied to interface 0/1 on Router-B with the following configuration:
The configuration of the default summary route on Router-B sends a 0.0.0.0/0 summary route to Router-C and blocks all other
routes, including the 10.1.1.0/24 route, from being advertised to Router-C. However, this configuration also generates a local
discard route on Router-B, a route for 0.0.0.0/0 to the null 0 interface with an administrative distance of 5. When this route
is created, it overrides the EIGRP learned default route. Router-B is no longer able to reach destinations that it would normally
reach through the 0.0.0.0.0/0 route.
This problem is resolved by applying a floating summary route to the interface on Router-B that connects to Router-C. The
floating summary route is applied by relating an administrative distance to the default summary route on the interface of
Router-B with the following statement:
The administrative distance of 250, applied in the above statement, is now assigned to the discard route generated on Router-B.
The 0.0.0.0/0, from Router-A, is learned through EIGRP and installed in the local routing table. Routing to Router-C is restored.
If Router-A loses the connection to Router-B, Router-B continues to advertise a default route to Router-C, which allows traffic
to continue to reach destinations attached to Router-B. However, traffic destined for networks to Router-A or behind Router-A
is dropped when the traffic reaches Router-B.
shows a network with two connections from the core: Router-A and Router-D. Both routers have floating summary routes configured
on the interfaces connected to Router-C. If the connection between Router-E and Router-C fails, the network continues to operate
normally. All traffic flows from Router-C through Router-B to the hosts attached to Router-A and Router-D.
However, if the link between Router-D and Router-E fails, the network may dump traffic into a black hole because Router-E
continues to advertise the default route (0.0.0.0/0) to Router-C, as long as at least one link (other than the link to Router-C)
to Router-E is still active. In this scenario, Router-C still forwards traffic to Router-E, but Router-E drops the traffic
creating the black hole. To avoid this problem, you should configure the summary address with an administrative distance on
only single-homed remote routers or areas in which only one exit point exists between the segments of the network. If two
or more exit points exist (from one segment of the network to another), configuring the floating default route can cause a
black hole to form.
Split Horizon for an EIGRP Process
Split horizon controls the sending of EIGRP update and query packets. When split horizon is enabled on an interface, update
and query packets are not sent for destinations for which this interface is the next hop. Controlling update and query packets
in this manner reduces the possibility of routing loops.
By default, split horizon is enabled on all interfaces.
Split horizon blocks route information from being advertised by a router on any interface from which that information originated.
This behavior usually optimizes communications among multiple routing devices, particularly when links are broken. However,
with nonbroadcast networks (such as Frame Relay and SMDS), situations can arise for which this behavior is less than ideal.
For these situations, including networks in which you have EIGRP configured, you may want to disable split horizon.
Adjustment of Hello Interval and Hold Time for an EIGRP Process
You can adjust the interval between hello packets and the hold time.
Routing devices periodically send hello packets to each other to dynamically learn of other routers on their directly attached
networks. This information is used to discover neighbors and learn when neighbors become unreachable or inoperative. By default,
hello packets are sent every 5 seconds.
You can configure the hold time on a specified interface for a particular EIGRP routing process designated by the autonomous
system number. The hold time is advertised in hello packets and indicates to neighbors the length of time they should consider
the sender valid. The default hold time is three times the hello interval, or 15 seconds.
Stub Routing for an EIGRP Process
The EIGRP Stub Routing feature improves network stability, reduces resource usage, and simplifies stub router configuration.
Stub routing is commonly used in a hub-and-spoke network topology. In a hub-and-spoke network, one or more end (stub) networks
are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router
is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through
a distribution router. This type of configuration is commonly used in WAN topologies in which the distribution router is directly
connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router is
connected to 100 or more remote routers. In a hub-and-spoke topology, the remote router must forward all nonlocal traffic
to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table. Generally, the
distribution router need not send anything more than a default route to the remote router.
When using the EIGRP Stub Routing feature, you need to configure the distribution and remote routers to use EIGRP and configure
only the remote router as a stub. Only specified routes are propagated from the remote (stub) router. The stub router responds
to all queries for summaries, connected routes, redistributed static routes, external routes, and internal routes with the
message “inaccessible.” A router that is configured as a stub sends a special peer information packet to all neighboring routers
to report its status as a stub router.
Any neighbor that receives a packet informing it of the stub status does not query the stub router for any routes, and a router
that has a stub peer does not query that peer. The stub router depends on the distribution router to send the proper updates
to all peers.
The stub routing feature by itself does not prevent routes from being advertised to the remote router. In the example in Figure 1 , the remote router can access the corporate network and the Internet through the distribution router only. Having a full
route table on the remote router, in this example, would serve no functional purpose because the path to the corporate network
and the Internet would always be through the distribution router. The larger route table would only reduce the amount of memory
required by the remote router. Bandwidth and memory can be conserved by summarizing and filtering routes in the distribution
router. The remote router need not receive routes that have been learned from other networks because the remote router must
send all nonlocal traffic, regardless of destination, to the distribution router. If a true stub network is desired, the distribution
router should be configured to send only a default route to the remote router. The EIGRP Stub Routing feature does not automatically
enable summarization on the distribution router. In most cases, the network administrator needs to configure summarization
on the distribution routers.
Without the stub feature, even after the routes that are sent from the distribution router to the remote router have been
filtered or summarized, a problem might occur. If a route is lost somewhere in the corporate network, EIGRP could send a query
to the distribution router, which in turn sends a query to the remote router even if routes are being summarized. If there
is a problem communicating over the WAN link between the distribution router and the remote router, an EIGRP stuck in active
(SIA) condition could occur and cause instability elsewhere in the network. The EIGRP Stub Routing feature allows a network
administrator to prevent queries from being sent to the remote router.
Route Policy Options for an EIGRP Process
Route policies comprise series of statements and expressions that are bracketed with the route-policy and end-policy keywords. Rather than a collection of individual commands (one for each line), the statements within a route policy have
context relative to each other. Thus, instead of each line being an individual command, each policy or set is an independent
configuration object that can be used, entered, and manipulated as a unit.
Each line of a policy configuration is a logical subunit. At least one new line must follow the then, else, and end-policy keywords. A new line must also follow the closing parenthesis of a parameter list and the name string in a reference to an
AS path set, community set, extended community set, or prefix set (in the EIGRP context). At least one new line must precede
the definition of a route policy or prefix set. A new line must appear at the end of a logical unit of policy expression and
may not appear anywhere else.
This is the command to set the EIGRP metric in a route policy:
RP/0/RSP0/CPU0:router(config-rpl)# set eigrp-metric bandwidth delay reliability loading mtu
This is the command to provide EIGRP offset list functionality in a route policy:
RP/0/RSP0/CPU0:router(config-rpl)# add eigrp-metric bandwidth delay reliability loading mtu
A route policy can be used in EIGRP only if all the statements are applicable to the particular EIGRP attach point. The following
commands accept a route policy:
default-information allowed—Match statements are allowed for destination. No set statements are allowed.
route-policy—Match statements are allowed for destination, next hop, and tag. Set statements are allowed for eigrp-metric and tag.
redistribute—Match statements are allowed for destination, next hop, source-protocol, tag and route-type. Set statements are allowed for
eigrp-metric and tag.
The range for setting a tag is 0 to 255 for internal routes and 0 to 4294967295 for external routes.
EIGRP Layer 3 VPN PE-CE Site-of-Origin
The EIGRP MPLS and IP VPN PE-CE Site-of-Origin (SoO) feature introduces the capability to filter Multiprotocol Label Switching
(MPLS) and IP Virtual Private Network (VPN) traffic on a per-site basis for EIGRP networks. SoO filtering is configured at
the interface level and is used to manage MPLS and IP VPN traffic and to prevent transient routing loops from occurring in
complex and mixed network topologies.
Interoperation with the Site-of-Origin Extended Community
The configuration of
the SoO extended community allows routers that support this feature to identify
the site from which each route originated. When this feature is enabled, the
EIGRP routing process on the PE or CE router checks each received route for the
SoO extended community and filters based on the following conditions:
A received route from BGP or
a CE router contains a SoO value that matches the SoO value on the receiving
If a route is
received with an associated SoO value that matches the SoO value that is
configured on the receiving interface, the route is filtered out because it was
learned from another PE router or from a backdoor link. This behavior is
designed to prevent routing loops.
A received route from a CE router is
configured with a SoO value that does not match:
If a route is
received with an associated SoO value that does not match the SoO value that is
configured on the receiving interface, the route is accepted into the EIGRP
topology table so that it can be redistributed into BGP.
If the route
is already installed in the EIGRP topology table but is associated with a
different SoO value, the SoO value from the topology table is used when the
route is redistributed into BGP.
A received route
from a CE router does not contain a SoO value:
If a route is
received without a SoO value, the route is accepted into the EIGRP topology
table, and the SoO value from the interface that is used to reach the next-hop
CE router is appended to the route before it is redistributed into BGP.
When BGP and EIGRP
peers that support the SoO extended community receive these routes, they also
receive the associated SoO values and pass them to other BGP and EIGRP peers
that support the SoO extended community. This filtering is designed to prevent
transient routes from being relearned from the originating site, which prevents
transient routing loops from occurring.
with BGP cost community, EIGRP, BGP, and the RIB ensure that paths over the
MPLS VPN core are preferred over backdoor links.
For MPLS and IP VPN
and SoO configuration information, see
MPLS Layer 3 VPNs in the
Cisco ASR 9000 Series
Aggregation Services Router MPLS
using SoO match condition
The SoO configuration
in EIGRP network can be used to manipulate routes using the SoO match condition
in the routing policy. The egress interface of a PE router is used to compare
and manipulate routes based on the SoO configuration on the remote PE router.
In the following
topology, CE1, CE2 and CE3 are the customer edge routers. PE1 and PE2 are the
provider edge routers. By default, CE1 will use PE1->PE2 to reach CE3.To
configure CE1 to use CE2 to reach CE3, the metric advertised by PE1 must be
The routing policy
on PE1 manipulates routes received from CE3 via PE2, by using the SoO match
condition. With this feature added, PE1 can increase the metric while
advertising routes to CE1.
/*SoO tag is assigned on PE2 router*/
router (config-if)#site-of-origin 220.127.116.11:33
/* A route-policy defined on PE1 */
router(config-rpl)#if extcommunity soo matches-any (18.104.22.168:33) then
router(config-rpl-if)#set eigrp-metric 2121212121 333333333 245 250 1455
router (config-if)#route-policy test out
/*A route with poor metric advertised by PE1 is installed into CE1’s routing table for SoO of site C3. */
router#show eigrp topology 6:6::1/128
IPv6-EIGRP AS(100): Topology entry for 6:6::1/128
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 15539149614794, RIB is 4294967295 Routing Descriptor Blocks: fe80::226:98ff:fe24:5109 (GigabitEthernet0/0/0/15), from fe80::226:98ff:fe24:5109, Send flag is 0x0
Composite metric is (15539149614794/15539148304382), Route is Internal Vector metric:
Minimum bandwidth is 1000000 Kbit
Total delay is 237108596182784 picoseconds
Reliability is 245/255
Load is 250/255
Minimum MTU is 1455
Hop count is 2
Originating router is 22.214.171.124
This feature is
applicable to both ipv4 as well as ipv6.
All types of
SoO(IP-Address, ASN2, ASN4) are supported.
EIGRP v4/v6 Authentication Using Keychain
EIGRP authentication using keychain introduces the capability to authenticate EIGRP protocol packets on a per-interface basis.
The EIGRP routing authentication provides a mechanism to authenticate all EIGRP protocol traffic on one or more interfaces,
based on Message Digest 5 (MD5) authentication.
The EIGRP routing authentication uses the Cisco IOS XR software security keychain infrastructure to store and retrieve secret keys and to authenticate incoming and outgoing traffic on a
EIGRP Wide Metric
The Cisco IOS XR
Enhanced Interior Gateway Routing Protocol (EIGRP) implementation is enhanced
to perform wide metric computation. This enhancement is to support high
A new EIGRP command is
added and existing EIGRP commands are enhanced to support wide metric
metric rib-scale—This command was introduced.
keyword was added.
metric weights—Support was added for the
show eigrp interfaces—The command output was
modified to display relevant wide metric information.
show eigrp neighbors —The command output was
modified to display relevant wide metric information.
show eigrp topology—The command output was
modified to display relevant wide metric information.
show protocols—The command output was modified to
display relevant wide metric information.
If there is a
combination of IOS and IOS-XR PE devices in the network, then the EIGRP wide
metric must be disabled in IOS-XR PE device. This is because the method of
calculating metrics in L3VPN design between IOS and IOS-XR.
The Enhanced Interior Gateway Routing Protocol (EIGRP) Multi-Instance feature allows multiple process instances to handle
different routing instances and service the same VRF. Each process instance handles the routing instances configured under
it. The multiple EIGRP process instance implementation allows to configure the EIGRP using a virtual-name in addition to an
EIGRP Support for
Bidirectional forwarding detection (BFD) for link failure detection.
BFD provides low-overhead,
short-duration detection of failures in the path between adjacent forwarding
engines. BFD allows a single mechanism to be used for failure detection over
any media and at any protocol layer, with a wide range of detection times and
overhead. The fast detection of failures provides immediate reaction to failure
in the event of a failed link or neighbor.
How to Implement EIGRP
This section contains instructions for the following tasks:
To save configuration changes, you must commit changes when the system prompts you.
This task enables
EIGRP routing and establishes an EIGRP routing process.
Before you begin
Although you can
configure EIGRP before you configure an IP address, no EIGRP routing occurs
until at least one IP address is configured.
Command or Action
RP/0/RSP0/CPU0:router(config)# router eigrp 100
autonomous system number of the routing process to configure an EIGRP routing
Configures a router-id for an EIGRP process.
It is good
practice to use the
router-id command to explicitly specify a unique
32-bit numeric value for the router ID. This action ensures that EIGRP can
function regardless of the interface address configuration.
Configures the hold time for an interface.
nonstop forwarding during RP failovers, as the number of neighbors increase, a
higher holdtime than the default value is recommended. With 256 neighbors
across all VRFs, we recommend 60 seconds.
Configures the percentage of bandwidth that may be used by EIGRP on an
Summarization for an EIGRP Process
This task configures
route summarization for an EIGRP process.
You can configure a
summary aggregate address for a specified interface. If any more specific
routes are in the routing table, EIGRP advertises the summary address from the
interface with a metric equal to the minimum of all more specific routes.
Before you begin
You should not use
summarization command to generate the default route (0.0.0.0)
from an interface. This command creates an EIGRP summary default route to the
null 0 interface with an administrative distance of 5. The low administrative
distance of this default route can cause this route to displace default routes
learned from other neighbors from the routing table. If the default route
learned from the neighbors is displaced by the summary default route or the
summary route is the only default route present, all traffic destined for the
default route does not leave the router; instead, this traffic is sent to the
null 0 interface, where it is dropped.
way to send only the default route from a given interface is to use a
RP/0/RSP0/CPU0:router(config-eigrp-af)# route-policy IN-IPv4 in
routing policy to updates advertised to or received from an EIGRP neighbor.
Routing for an EIGRP Process
This task configures
the distribution and remote routers to use an EIGRP process for stub routing.
Before you begin
EIGRP stub routing
should be used only on remote routers. A stub router is defined as a router
connected to the network core or distribution layer through which core transit
traffic should not flow. A stub router should not have any EIGRP neighbors
other than distribution routers. Ignoring this restriction causes undesirable
site-of-origin (SoO) filtering on the EIGRP interface.
Routes into EIGRP
Perform this task to
redistribute BGP routes into EIGRP.
routes are redistributed into BGP with extended community information appended
to the route. BGP carries the route over the VPN backbone with the
EIGRP-specific information encoded in the BGP extended community attributes.
After the peering customer site receives the route, EIGRP redistributes the BGP
route then extracts the BGP extended community information and reconstructs the
route as it appeared in the original customer site.
BGP routes into EIGRP, the receiving provider edge (PE) EIGRP router looks for
BGP extended community information. If the information is received, it is used
to recreate the original EIGRP route. If the information is missing, EIGRP uses
the configured default metric value.
If the metric values
are not derived from the BGP extended community and a default metric is not
configured, the route is not advertised to the customer edge (CE) router by the
PE EIGRP. When BGP is redistributed into BGP, metrics may not be added to the
BGP prefix as extended communities; for example, if EIGRP is not running on the
other router. In this case, EIGRP is redistributed into BGP with a “no-metrics”
all EIGRP protocol traffic on the interface, based on the MD5 algorithm.
EIGRP typically broadcasts or
multicasts routing updates. For security reasons, you can opt to configure
static neighbors in the EIGRP routing process, forcing EIGRP to communicate to
specified neighbors using unicast. When you specify a static neighbor
relationship over a particular interface, EIGRP disables the processing of
multicast EIGRP packets on the specified interface. This ensures that EIGRP
does not send nor process received multicast EIGRP traffic on an interface
which has a static neighbor defined under the EIGRP routing process.
In cases where the
neighbors are not adjacent, normal EIGRP peering mechanisms cannot be used to
exchange EIGRP information. In order to support this type of network, EIGRP
provides the neighbor command, which allows remote neighbors to be configured
and sessions established though unicast packet transmission. However, as the
number of forwarders needing to exchange EIGRP information over the networking
cloud increases, unicast EIGRP neighbor definitions may become cumbersome to
manage. Each neighbor must be manually configured, resulting in increased
operational costs. To better accommodate deployment of these topologies, ease
configuration management, and reduce operational costs, the Dynamic Neighbors
feature provides support for the dynamic discovery of remote unicast (referred
to as “remote neighbors”). Remote neighbor support allows EIGRP peering to one
or more remote neighbors, which may not be known at the time the device is
configured, thus reducing configuration management.
In the topology illustrated
below, ASA behaves as a hub and the other routers (2921s, 7010s) act as spokes.
The 2921's and 7010's must not peer with each other, and there must never be a
time where a packet (data traffic) is routed in this path: ASA > 2921.3 >
2921.4. To support this type of network, EIGRP allows you to configure static
neighbors and establish sessions using unicast packet transmission. Thus, in
this topology, 2921s and 7010s peer with ASA using neighbor command and ASA is
configured to dynamically discover remote neighbors.
When using remote unicast-listen or
remote multicast-group neighbor configurations, EIGRP neighbor IP addresses are
not predefined, and neighbors may be many hops away. A device with this
configuration could peer with any device that sends a valid HELLO packet.
Because of security considerations, this open aspect requires policy
capabilities to limit peering to valid devices and to restrict the number of
neighbors in order to limit resource consumption. This capability is
accomplished using the following manually configured parameters, and takes
Neighbor Filter ListThe optional allow-list keyword, available in the remote-neighbors
command, enables you to use an access list (access control list) to specify the
remote IP addresses from which EIGRP neighbor connections may be accepted. If
you do not use the allow-list keyword, then all IP addresses (permit any) will
be accepted. The access control list (ACL) defines a range of IPv4 or IPv6 IP
addresses with the following conditions:
Any neighbor that has a
source IP address that matches an IP address in the access list will be allowed
(or denied) based on the user configuration.
If the allow-list
keyword is not specified, any IP address will be permitted (permit any).
The allow-list keyword
is supported only for remote multicast-group and unicast-listen neighbors. It
is not available for static, remote static, or local neighbors.
Incoming EIGRP packets
that do not match the specified access list will be rejected.
NeighborsThe optional max-neighbors keyword, available in the
remote-neighbors command, enables you to specify a maximum number of remote
neighbors that EIGRP can create using the remote neighbor configurations. When
the maximum number of remote neighbors has been created for a configuration,
EIGRP rejects all subsequent connection attempts for that configuration. This
option helps to protect against denial-of-service attacks that attempt to
create many remote neighbors in an attempt to overwhelm device resources. The
max-neighbors configuration option has the following conditions:
This option is supported
only for remote multicast-group or unicast-listen neighbors. It is not
available for local, static, or remote static neighbors.
There is no default
maximum. If you do not specify a maximum number of remote neighbors, the number
of remote neighbors is limited only by available memory and bandwidth.
Reducing the maximum
number of remote neighbors to less than the current number of sessions will
result in the neighbors (in no specific order) being dropped until the count
reaches the new limit.
Configuration Changes for
the Neighbor Filter List and Maximum Number of Remote Neighbors
When the allow-list or max-neighbors configurations are changed, any
existing remote EIGRP sessions that are no longer allowed by the new
configuration will be removed automatically and immediately. Pre-existing
neighbors that are still allowed by the new configuration will not be affected.
The following terms
are used when describing neighbor types:
local neighbor: A
neighbor that is adjacent on a shared subnet (or common subnet) and uses a
link-local multicast address for packet exchange. This is the default type of
neighbor in EIGRP.
static Neighbor: Any
neighbor that uses unicast to communicate, is one hop away, is on a common
subnet, and whose IP address has been specified using the neighbor ip-address
remote neighbor: Any
neighbor that is multiple hops away, including Remote Static Neighbors.
remote group: Any
neighbor that is multiple hops away, does not have its address manually
configured with the neighbor command and uses the multicast group address for
remote static neighbor:
Any neighbor that uses unicast to communicate, is multiple hops away, and whose
IP address has been specified using the neighbor ip-address command.
remote unicast-listen (or
simply unicast-listen): Any neighbor that uses unicast to communicate, is
multiple hops away, and whose IP address has not been configured using the
neighbor ip-address command.
remote dnyamic: Any
neighbor that is multiple hops away and whose address has not been configured
with the neighbor ip-address command, that is, a remote multicast-group or
remote unicast-listen neighbor, but not a remote static neighbor.
Unicast-Listen (Point-to-Point) Neighbors
For configurations in
which multiple remote neighbors peer with a single hub (point-to-point), the
hub can be configured for remote unicast-listen peering using the
remote-neighbors command to allow the remote neighbors to peer with the hub
without having to manually configure the remote neighbor IP addresses on the
hub. When configured with this command, the hub device:
Uses its interface IP address
as the source IP address for any unicast transmissions. This IP address must be
Requires neighbors that peer
with the hub to be configured using the neighbor ip-address loopback
loopback-interface-number remote maximum-hops command where ip-address is the
unicast address of the local device interface.
Listens for unicast HELLO
packets on the interface specified in the remote-neighbor command.
Accepts a unicast HELLO
packet if it is in the IP address range configured using the allow-list
keyword, or any unicast HELLO packet if an allow list is not defined.
Rejects multicast HELLO
packets from any neighbor that is also sending unicast HELLO packets and is
permitted by the unicast allow list (or all neighbors if an allow list is not
Begins normal neighbor
establishment using the IP addresses of the remote neighbors for packet
transmission once the neighbor relationship is established.
When remote-neighbor command
is configured on an interface, the router will only start sending HELLOs on
that interface if it has atleast one neighbor and only to those neighbors from
which it has received HELLOs.
On an interface if dynamic
neighbors already exist and remote-neighbor unicast- listen is configured, then
the existing neighbor relationships will be torn down and only unicast-neighbor
relationships will be allowed there after.
A single unicast address can only be
configured to a single remote static neighbor for a given address-family. You
cannot configure a second remote static neighbor using the same unicast
address, on a different interface. EIGRP configuration of remote neighbors
under different address families is unrestricted.
A single interface can be configured under a single address family with
a single unicast-listen remote-neighbors command and with any number of static
and remote static neighbors (each using a different unicast address).
precedence of the remote neighbor configurations
Static neighbors configured with the
<address> or neighbor
<address> remote commands take precedence over the remote
neighbors created as a result of the remote-neighbors command. If the remote
address of an incoming unicast EIGRP connection matches both a static neighbor
and the remote unicast-listen neighbor access list, the static neighbor is used
and no remote unicast-listen neighbor is created. If you configure a new static
neighbor while a remote neighbor for the same remote address already exists,
EIGRP automatically removes the remote unicast-listen neighbor.
How to configure
remote unicast neighbors
When configuring an
EIGRP unicast neighbor, the neighbor statement is required on both ends (hub
and spoke) of the neighbor relationship in the EIGRP routing process that
operate in the same autonomous system.
Before you begin
Ensure that when
using unicast-listen mode, IP connectivity (reachability) exists between
devices that need to do remote peering.
EGRP process that enables remote neighbors to accept inbound connections from
any remote IP address.
allow-list keyword to use
an access list (access control list) to specify the remote IP addresses from
which EIGRP neighbor connections may be accepted. If you do not use the allow
list keyword, all IP addresses will be accepted.
max-neighbors keyword to
specify the maximum number of remote neighbors. If you do not specify a number,
the maximum number of remote neighbors is limited only by available memory and
sh run router eigrp
EIGRP remote unicast neighbors
examples show how to configure both devices (hub and spoke) involved in the
This section provides the following configuration examples:
Configuring a Basic EIGRP Configuration: Example
The following example shows how to configure EIGRP with a policy that filters incoming routes. This is a typical configuration
for a router that has just one neighbor, but advertises other connected subnets.
Configuring an EIGRP PE-CE Configuration with Prefix-Limits: Example
The following example shows how to configure EIGRP to operate as a PE-CE protocol on a PE router. The configuration is under
VRF CUSTOMER_1. A maximum prefix is typically configured to ensure that one set of customer routes do not overwhelm the EIGRP
No new or
modified RFCs are supported by this feature, and support for existing standards
has not been modified by this feature.
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