Configure the confederation identifier using the bgp confederation identifier command

Step 3. Configure fully meshed iBGP sub-AS neighbor relationships using the sub-AS number as the remote AS number (ASN) for all internal iBGP peers.

Step 4. Configure other neighbors within the same parent AS by specifying their sub-AS number as the remote AS number; other confederation peers from different sub-ASs must also be identified as external confed-eration peers using the bgp confedconfed-eration peers command.

Step 5. Configure any eBGP neighbors as you normally would.

Peer Groups

To configure one router with multiple BGP peer relationships, configurations can be quite complex. Peer groups simplify the configuration process. You make peer groups and assign neighbors with the same policies to the group.

Peer group members inherit the policies assigned to the group.

To configure BGP peer groups on Cisco IOS routers, complete the following steps:

Step 1. Create a BGP peer group; use the neighbor peer-group router configuration command.

Step 2. Specify parameters for the BGP peer group.

Step 3. Create a BGP neighbor.

Step 4. Assign a neighbor to the peer group; use the neighbor peer-group router configuration command.

network backdoor Command

The network backdoor router configuration command causes the administrative distance assigned to the network to be forced to 200. The goal is to make IGP-learned routes preferred. A network marked as a backdoor is not sourced by the local router, but should be learned from external neighbors. You should be sure to verify the route is in the BGP table for the command to have the desired effect.

Configuring the BGP maximum-prefix Function

To control how many prefixes a BGP router can receive from a neighbor, use the neighbor maximum-prefix router configuration command.

Route Dampening

Flapping routes create problems for BGP. An approach was created to remove the update about a flapping route until it can be guaranteed that the destination is more stable. This additional BGP scalability mechanism, called route flap dampening, was created to reduce route update processing requirements by suppressing unstable routes.

To enable route dampening, use the bgp dampening command.

Troubleshooting and Monitoring BGP

Important commands not included elsewhere in the BGP Short Cuts include the following:

n show ip bgp neighbors ip-address:Displays detailed neighbor information

n show ip bgp: Displays all the routes in the BGP table

n show ip bgp ip-prefix [mask subnet-mask]: Displays detailed information about all paths for a single prefix

n debug ip tcp transactions: Displays all TCP transactions

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n debug ip bgp events:Displays significant BGP events

n debug ip bgp keepalives: Debugs BGP keepalive packets

n debug ip bgp updates: Displays all incoming or outgoing BGP updates

n debug ip bgp updates acl:Displays all incoming and sent updates matching an ACL

n debug ip bgp ip-address updates [acl]: Displays all BGP updates received from or sent to a specific neighbor

EIGRP

Enhanced Interior Gateway Routing Protocol (EIGRP) is a hybrid routing protocol—combining features of both distance vector and link-state routing protocols. Advantages include the following:

n VLSM support

n Rapid convergence thanks to Diffusing Update Algorithm (DUAL)

n Low CPU utilization—with typically only hellos and partial updates being sent on a link

n Incremental updates

n Scalability

n Ease of configuration

n Automatic route summarization, or manual route summarization

n MD5 route authentication

EIGRP uses IP protocol 88. It uses a multicast address of 224.0.0.10 for hellos and routing updates.

EIGRP’s Metric

EIGRP uses a composite metric such as Interior Gateway Routing Protocol (IGRP), but it is modified with a multiplier of 256. Bandwidth and delay are the defaults enabled. EIGRP calls the metric feasible distance. All the possible metric values are as follows:

n Bandwidth:Expressed in kilobytes; to adjust the bandwidth value assigned to an interface, use the band-width command.

n Delay:Expressed in microseconds; it can be adjusted using the delay command; when manipulating met-rics, consider delay because bandwidth would affect other protocols, too.

n Reliability: Expressed as a number in the range of 1 to 255; 1 is a completely unreliable link.

n Load: Expressed as a number in the range of 1 to 255; 1 is a minimally loaded link.

n MTU: Maximum transmission unit; the smallest recorded MTU in the path. Note that MTU is not used in metric calculation.

The metric formula used by EIGRP is as follows:

metric = [K1 * BW + ((K2 * BW) / (256 – load)) + K3 * delay]

By default, K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0.

If you manipulate the K values on one router, you must manipulate on all.

EIGRP uses a 32-bit metric as opposed to the 24-bit metric of IGRP; the two are compatible automatically during redistribution, however.

EIGRP Packets

n Hello:Establish neighbor relationships.

n Update: Send routing updates.

n Query:Ask neighbors about routing information.

n Reply: Respond to queries.

n Ack: Acknowledge reliable packets.

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The address used for hello packets is 224.0.0.10; AS numbers must match. Hellos are sent every 5 seconds on broadcast links and point-to-point serial links, point-to-point subinterface links, and multipoint circuits greater than T1. They are sent every 60 seconds on other link types. The hold time defaults to 3 times the hello time.

Neighborships form even if the values do not match.

EIGRP Reliability

Packets that require acknowledgment are as follows:

n Update

n Query

n Reply

Packet that do not are as follows:

n Hello

n Ack

Neighbor reset after retry limit (16) is reached. Slow neighbors are sent unicast packets instead.

Initial Route Discovery

Router discovery and route exchange happen simultaneously as follows:

1. Router comes up and sends hellos.

2.Reply from a neighbor includes Update.

3.Ack packets are sent.

4.Update process occurs in the opposite direction.