EIGRP & EIGRP6

EIGRP:

·       route entries are classified into 3 groups.

o    Interior routes, aka local to the major network to which the advertising and receiving routers are connected. 192.168.2.192/26 is advertised to 192.168.2.64/26 with the same AS as an interior route because it falls within the same major network.

o    System routes, a path to a network address that has ben summarized by a network boundary router.  192.168.3.0 is advertised to 192.168.2.0 within the same AS as a system route.

o    Exterior routes, A path to a default network, or a network in another autonomous system.

·       EIGRP calculates all metrics from outgoing interfaces only.

·       Composite metric is the minimum bandwidth of an outgoing interface, the cumulative delay, load, reliability, and smallest MTU along a path.

·       Default metric = 256(10^7/(min(BW)) + (sum(DLAY)/10)

distribute-list gateway {prefix-list} {in|out} {interface}   # filters all routes to/from a neighbor.

#interface s0/0/0

  #bandwidth 128

  #ip bandwidth-percent eigrp 1 200 # adjusts EIGRP bandwidth to %200 which is 256K.

EIGRP packet delivery is handled using Reliable Transport Protocol (RTP) which ensures delivery in order using Reliable Multicast on the multicast address 224.0.0.10. EIGRP uses IP protocol number 88. Unequal cost load balancing up to 16 links.

Unlike IGRP, in the IP environment, EIGRP is a Classless routing protocol since updates carry subnet mask information. Although EIGRP automatically summarizes on the network boundary, it can be configured to summarize on any bit boundary. EIGRP can also be used when aggregating routes i.e. when summarizing major networks.

EIGRP uses the Neighbor Table to list adjacent routers. The Topology Table lists all the learned routes to a destination whilst the Routing Table contains the best route to a destination, which is known as the Successor. The Feasible Successor is a backup route to a destination which is kept in the Topology Table.

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.  Neighbors should always form when these conditions are met, regardless of link type.

·       Must pass the authentication process

·       Must use the same configured AS number

·       Must have the source IP address of a received Hello is in that router’s primary connected subnet on that interface

·       K values must match

If one router has configured 10.1.2.1/24, and the other has configured 10.1.2.2/23, they could become adjacent, assuming all the other checks pass. While EIGRP supports secondary IP addresses and subnets, EIGRP sources its messages from the address in the primary subnet, and the IP addresses of neighbors must be in the subnet of the primary subnets.

Interestingly, the Hello and Hold time parameters do not need to match for EIGRP neighbor relationships to form. In fact, a router does not use its own timers when monitoring a neighbor relationship—instead, it uses each neighbor’s stated timers, as exchanged in the Hello messages.

EIGRP uses the Reliable Transport Protocol (RTP) to send the multicast EIGRP updates. EIGRP sends updates, waiting on a unicast EIGRP ACK message from each recipient.  The delay command’s units are tens of microseconds. A delay 1 command sets the interface delay as 10 microseconds

Update packet has the Init bit set to 1 means EIGRP neighbor will restart the session if it already had an established relationship with the neighbor.  Eigrp Stub router is not queried for any routes, but sends/receives routes.

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 non-broadcast 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.

K values are constants that define the multipliers and used by EIGRP when calculating metrics. The settings can be changed with a router eigrp  metric weights TOS k1 k2 k3 k4 k5. The K value defaults to a setting of  0 1 0 1 0 0, meaning only bandwidth and delay are used to calculate the metric.

Link Cost == 256 ( (10^7/lowest BW in path) + (sum of Delay along the path) )

Stuck-in-active: router queries all neighboring routers ‘actively’ for a prefix/network and each neighboring router in turn actively querying their neighbors, so on and so forth && it never ends, so comes the ‘Active Timer’.  If the Active timer expires before a router receives all of its Reply messages, the router places the route in a stuck-in-active state. The router also brings down any neighbors from which no corresponding Reply was received, thinking that any neighbors that did not send a Reply are having problems. timers active-time disabled subcommand under router eigrp.

You can use route summarization which the neighbor will Reply or eigrp stub router; not to carry transit traffic.

 eigrp stub connected summary

Note that the stub option still requires the stub router to form neighbor relationships, even in receive-only mode. The stub router simply performs less work and reduces the query scope.

Feature	Description
Transport	IP, protocol type 88 (does not use UDP or TCP).
Metric	Based on bandwidth and cumulative delay by default, and optionally load, reliability, and MTU.
Hello interval	Interval at which a router sends EIGRP Hello messages on an interface.
Update destination address	Normally sent to 224.0.0.10, with retransmissions being sent to each neighbor’s unicast IP address.
Full or partial updates	Full updates are used when new neighbors are discovered; otherwise, partial updates are used.
Authentication	Supports MD5 authentication only.
VLSM/classless	EIGRP includes the mask with each route,  allowing it to support dis-contiguous networks and VLSM.
Route Tags	Allows EIGRP to tag routes as they are redistributed into EIGRP.
Next-hop field	Supports the advertisement of routes with a different next-hop router than the advertising router.
Manual route summarization	Allows route summarization at any point in the EIGRP network.
Multiprotocol	Supports the advertisement of IPX and AppleTalk routes.
Hold timer	Timer used to determine when a neighboring router has failed, based on a router not receiving any EIGRP messages, including Hellos, in this timer period.

The EIGRP term “active” refers to a route for which a router is currently using the Query process to find a loop-free alternative route. Conversely, a route is in passive state when it is not in an active state.

Query messages use reliable transmission via RTP and are multicasts; Reply messages are reliable and are unicasts. Both are acknowledged using Ack messages.

EIGRP offset lists allow EIGRP to add to a route’s metric, either before sending an update, or for routes received in an update. The offset list refers to an ACL (standard, extended, or named) to match the routes; any matched routes have the specified offset, or extra metric, added to their metrics. Any routes not matched by the offset list are unchanged. The offset list also specifies which routing updates to examine by specifying a direction (in or out) and, optionally, an interface.

If the interface is omitted from the command, all updates for the defined direction will be examined.

key chain must have the same key number for the neighbor to come up:

R4#sh ipv eig 1 int

IPv6-EIGRP interfaces for process 1

                        Xmit Queue   Mean   Pacing Time   Multicast    Pending

Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes

Gi0/1              0        0/0         0       0/1           50           0

Se0/0/0            1        0/0       129       0/15         623           0

Se0/0/1            1        0/0        20       0/15          99           0

Lo100              0        0/0         0       0/1            0           0

R4#sh key chain

Key-chain EIGRP:

    key 0 -- text "CISCO"

        accept lifetime (always valid) - (always valid) [valid now]

        send lifetime (always valid) - (always valid) [valid now]

R4#config t

Enter configuration commands, one per line.  End with CNTL/Z.

R4(config)#no key chain EIGRP 

R4(config)#key chain EIGRP

R4(config-keychain)#key 1 

R4(config-keychain-key)#key-string CISCO

R4(config-keychain-key)#end

May 13 05:40:38.697: %DUAL-5-NBRCHANGE: IPv6-EIGRP(0) 1: Neighbor FE80::21C:F6FF:FE1D:43D0 (GigabitEthernet0/1) is up: new adjacencyMay 13 05:40:39.521: %SYS-5-CONFIG_I: Configured from console by console

R4#

• EIGRP and Frame-relay need to use broadcast keyword in the frame map statements. Without broadcast keyword the adjacency will not form.
• Don’t forget to disable split horizon on the hub no ip split-horizon eigrp
• adjusting delay can manipulate the Eigrp Path.
• eigrp uses the minimum bandwidth on the path to a destination network and the total delay to compute routing metrics.
•  bandwidth = 1,000,000/bandwidth(i))*256  – where (i) is the lowest bandwidth of all outgoping interfaces on the route to the destination represented in kilobits.
• delay = delay(i) *256  – where (i) is the sum of the delays configured on the interfaces on the route to the destination network in tens of microseconds, so you must divide by 10 before you use it in this formula. 
• EIGRP does not build peer relationships over secondary addresses
• Eigrpv6: default route can be inject or purged (in/out) in two ways:
• redistribute-list, AD 170. 
• Ipv6 summary under interface, AD 90.  No leak-map though.  
• R6(config-subif)#ipv6 summary-address eig 1 0::/0 ?
    <1-255>  Administrative distance
    <cr>
   
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