EIGRP (Enhanced Interior Gateway Routing Protocol) is a Advance distance vector routing protocol used on computer network for best routing decision and configuration. The protocol was designed by Cisco System to use only on Cisco device but nowdays its open standard.
Before EIGRP routers can exchange routes with each other, they must become neighbors, and there are three conditions that must be met before this
can happen. And these three things will be exchanged with directly connected neighbors:
- Hello or ACK received
- AS numbers match
- Identical metrics (K values)
In Eigrp all the router must have same AS number. If AS number is not matching then no neighbor table will be created. And if authentication is applied then it should be matched.
in EIGRP router sends hello packets within every 5 sec to check wheather destination router is working or not. If hello doesnot come until 5 sec then the destination router is decleared as dead.
- Version 2
- Opcode : Hello
- Virtual Router ID
- Autonomous System (AS) 10
- Composite K parameters
- Software Version
DUAL (Diffusion Update Algorithm) is used by EIGRP. And it has a few term, lets know the term.
- SUCESSOR : The best path from source to destination with lowest metric is called Sucessor.
- FEASIBLE SUCESSOR : The secondary best path or backup path from source to destination is called Feasible Sucessor. To create a backup path router should fulfill feasible condition i.e Rd of backup path must be less then Fd of feasible Sucessor.
- FEASIBLE DISTANCE : The metric value of the path availale is called feasible Distance. If metric value is same for multiple path then eigrp will automatically load balance.
- REPORTED DISTANCE : The metric value from source's neighbour to destination is called Reported Distance.
r1# config t
r1# router eigrp 10 [enables eigrp process and 10 is AS number]
r1# network 192.168.1.0
r1# network 192.168.2.0
This simply enables EIGRP process and follow same on other
Few Important troubleshooting command as steps:
#show ip eigrp neighbors - Checking neighbor table
#show ip eigrp interfaces - Checking eigrp enable interface
#show ip route eigrp- Checking routing table
#show ip eigrp topology - Checking topology table
Sender router send a multicalt to all avail router in network and receives reply from all but if any particular router did not reply then a sender router will send 16 unicast to that particular router, if reply received then neighbourship will continue and if not then will declear as dead. Mainly the time difference between Multicast and Unicast is RTO.
If you want backup path along with best path when best path has a conjuction then unequal cost load balancing is performed. This is also called Variance.
Variance is always multiply with best paths FD and default is 1.
#router eigrp 10
#variance [Value /2]
when we multiply FD of best path and variance, the value come will logical and can not be seen and best path will be best and backup path will be added on routing table. Max 16 and default 4 path can be added on version 12.7 but in 15.0 can be added upto 32 path.
When router broadcasts the hello packet it broadcast towards all interface i.e router connected and lan connected but broadcasting towards lan
is wastage and bandwidth will consume so we can make those interface passive where do not need such packet. once interface is passive broadcast packet
will not go towards those interface but be sure that you are not making interface passive which is connected to another router which will cause the break
on eigrp neighborship.
#router eigrp 10
# passive-interface f0/0
It is of 32 bit as like ip address. router with same router id can communicate within same AS number but can not communicate between differet
AS number with same router id.
If router has a loopback then higest loopback will be routerID but if it does not have loopback then highest physical ip address will be routers router id. but it can be change and give manual id too.
#router eigrp 10
#router-id 126.96.36.199 (188.8.131.52 is router id)
Redistribution is the precess of exchangind information from one to another. redistribution can be done on that router which consist of both AS information and in our topology R1 consist of both AS information so we will redistribute on R1.
r2#router eigrp 10
r2#redistribute eigrp 20
r2#router eigrp 20
r2#redistribute eigrp 10