Routing Protocols: EIGRP

EIGRP

•      Fastest to converge (backup routes / goodbye messages)
•         Easiest to configure
•        Proprietary to CISCO
•     Default Hello time of 5 seconds, and Hold of 15
•         Only protocol that holds backup routes (DUAL)
• Feasible successor kept in topology table, and brought into routing table if successor route goes down.
•         Unequal cost load balancing
•          Considered distance vector (only knows what neighbor tells it), with attributes of link state.
•          “TO BE CONSIDERED A FEASIBLE SUCCESSOR, THE AD MUST BE LESS THAN THE FD OF THE SUCCESSOR.”
•          Active / Passive routes: 
•    Active: Actively trying to find a backup
•    Passive: Good / working / no actions happening.
•          Metric calculation:
•    BW=10^7 / BW
•    Delay= delay in microseconds
•    Metric=256(Slowest BW+ total delay)
•          Sh ip eigrp topology command: shows successors / feasible successor routes
•          Ip default-network (similar to default information originate like in OSPF) used to advertise default route in EIGRP  (HAS TO BE CLASSFUL).  Another method is to create a static route as 0.0.0.0 and advertise through EIGRP.
•          Passive-interface <interface> within eigrp config, will keep hello updates from being sent.
•    Can use passive-interface default to turn on passive-interface on all interfaces of the router.
•          Ip summary-address eigrp <AS #> <IP> <netmask> Used to summarize routes (sub interface command)
•          Always choose more specific route than any summarized route (even if using RIP over EIGRP, etc.)
•          Variance <number> command used to load balance.  Number is used to determine how packets are routed.  Example:  will load balance across links that are 2 times as bad as my primary, if using variance 2.  Looking at feasible distance of successor / feasible successors, we can see which routes will be used (if fits under multiplier).  

  Advanced EIGRP:

• Multipoint=same subnet, point to point=diff subnets
•          NBMA (Non-Broadcast Multiple access) used in place of broadcasts
•          Int s0/0.1 multipoint=used to create multipoint sub interface
•          Frame-relay map ip <distance ip> <local DLCI> broadcast
•          If use “neighbor “ command, disables multicast (neighbors cannot auto form)
•     Split Horizon is a feature EIGRP uses to prevent routing loops.  It prevents loops by not accepting routes on the same interface that a router sends updates out.  This can be useful, but can also keep your network from functioning as intended. 

•          If frame relay is configured on a physical interface, auto disables split horizon.  But with sub-interfaces, split horizon is enabled.
•          Only advantage of multipoint is saving of IP addresses (only need to configure one subnet, whereas point to point are on different subnets.  But other than that, point to point is more advantageous (no split horizon issues).
•          No ip split-horizon eigrp <AS#> used to disable split horizon (useful in multipoint frame relay networks.)   (used on interface subcommand)
•          Within interface subcommand, ip summary-address eigrp <as #> <summary ip address> Summary routes sent over particular interface.
•          Ip bandwidth-percent eigrp <AS#>  <percentage> percentage rate to which one would increase to (PERFORMED FROM INTERFACE SUBCOMMAND).   Default is 50%  (limited interface bandwidth, then divided by number of neighbors) 100kbps with 2 neighbors is only 25kbps per neighbor (50% of 100kbps divided between two neighbors)
•          Important to use NTP to keep time intervals correct.
•          From global config, key chain <name> .  Use key <number> to create keys.  From within the key interface, can use key-string <key-string#> to give the keys a string names.   Accept-lifetime <time day month year> <end time day month year (or infinite)>    Send-lifetime <time day month year> <end time day month year (or infinite)>
•          To turn on EIGRP authentication: go into interface, ip authentication mode eigrp <AS#> md5 (EIGRP ONLY USES MD5)
•          Ip authentication key-chain eigrp 25 <keychain name>  on each neighbor device
•          Debug eigrp packet is a useful tool to test authentication process.
•          Eigrp stub (used to label stub routers as a stub (helps with query process)
•          K value (bandwith, delay, reliability, load, MTU) used to calculate EIGRP metric.  If any K value differences, cannot create neighbor relationship
•          Graceful shutdown (goodbye message):  When anything done to affect EIGRP neighbor process, one final hello packet sent, setting K-values to 255       
•    Depending on IOS version; OLD=K-value mismatch, NEW=Goodbye received
•    Once goodbye message received on neighbor device, neighbor will automatically start looking for a backup route, instead of waiting on hold down timer to expire, meaning quicker convergence.