Wednesday, January 5, 2011

CCIE Study Guide: EIGRP Notes

This is the first among our CCIE Study Guide Series and attempts to guide you through EIGRP, with some study notes.

Cisco Proprietary Protocol
Advanced distance vector
Automatic summarization at classful boundary (can be disabled/turned off)
supports VLSM/CIDR
manually summarized routes have AD of 5, point to NULL0
more specific routes within summarized range must exist in routing table, or summarized route disappears
multicast address
Unicast and multicast are used for updates
IP/IPX/Appletalk routed protocol support
no special configuration required for various layer 2 technologies
Unequal cost load balancing
Successor - Best path to a destination
Feasible sucessor - second best path to a destination
Advertised Distance - cost from next hop to final destination
Feasible Distance - cost from local router to final destination
For Feasible successor to be used, AD must be less than the FD through successor
Hello Packets are sent every 5 seconds on links greater than T1
sent every 60 seconds for T1 and slower
hold time interval defaults to 3 times the hello interval
changing default hello interval does NOT automatically update the hold time
ip hello-interval eigrp {as} {seconds} interface command
ip hold-time eigrp {as} {seconds} interface command
Un-acknowledged multicast updates are unicast to the host that did not ack.  This avoids hold ups with further updates to the rest of the network
EIGRP metric is based on load, bandwidth, delay, and reliability.
Cisco recommends leaving k values at default
Configuration of EIGRP
router eigrp {as}
network {address | wildcard mask} (wildcard is optional)
no auto-summary (turns off summarization at classful boundary)
redistribute static (redistributes any static routes into the protocol)
variance {#} (modifies which routes will be considered for unequal cost load balancing)
max-paths {#} (number of paths to be used for load balancing. default is 4, max is 16)
ip summary-address eigrp {as} {address | mask} (interface configuration command to summarize routes at a non classful boundary.)
eigrp stub receive-only ( this creates a stub in eigrp.  The “receive-only option” tells the stub router to not send ANY routes)
EIGRP Authentication
EIGRP supports cleartext and MD5 authentication.  It looks like we’re only concerned with MD5 for the exams (for obvious security reasons)
ip authentication mode eigrp {as} md5 (interface config mode)
ip authentication key-chain eigrp {as} {name of keychain}

key chain {name of keychain} (global config mode)
key {key-id} (this can be between 0-2147483647)
key-string {key}

As of IOS 12.3, EIGRP sends a graceful goodbye message when bringing the process down.  Goodbye messages are sent inside of Hello packets

Helpful Commands
show ip eigrp neighbors
show ip route
show ip route eigrp
show ip protocols – shows active routing protocol info (displays k values)
show ip eigrp interfaces
show ip eigrp toplogy – successor/feasible successor
show ip eigrp traffic
debug eigrp packets
Key technologies
DUAL Finite State
Neighbor discovery/recovery
Protocol dependant modules (ip, ipx, appletalk)
Wait for all the other CCIE preparation notes, which are under preparation.

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