Sunday, February 12, 2017

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Common EIGRP Neighborship Formation Issues

                      EIGRP now it’s Open to other Vendors it’s very scalable, it convergences rapidly, we can do Unequal path Load-balancing with Variance, it’s got lots of feature and in this session we wanna take a look at Troubleshooting one of more common EIGRP issues that is, we got couple of Routers and they not forming a neighborship and in our next session we will take a look at another common EIGRP issue and that is, we are not Routing appropriately we are expecting about to show up and it’s not showing up, what’s going on
                   But here let’s take a look at couple of reason that neighborship might not form between couple of EIGRP speaking Routers
One reason is the interfaces that each end of this link interconnecting Routers are in different subnets, now this is a IPv4 issue most of the issues are gonna be discussing apply to both IPv4 and IPv6
                           Something else that could be wrong, is the interface administratively Shutdown we are not gonna be forming neighborship over and interface if that is Administratively Down
                    Maybe that interface is up but it’s not participating in the EIGRP Process, did we give an appropriate network statement for IPv4 anyway, to say that this interfaces participating in this EIGRP Process or with IPv6 did we go into the interface and say that this interface is participating in this EIGRP Routing Process
                 Interface Configured to be Passive remember what Passive interface does, a Passive interface can still have its network advertised by the EIGRP Routing Process but that Passive interface is not going to be sending EIGRP message, we are not gonna form a neighborship over an interface that’s operating a Passive mode
                   If we have Authentication enabled, we need to make sure that we got matching Credential are both sides
                Maybe we Filtering EIGRP Packets, we got some sort of an ACL an it’s blocking EIGRP Packets that would prevent neighborship forming between couple of Routers
              And something that really critical with EIGRP is that the Autonomous System Numbers have to equal between neighbors, we don’t wanna go to one Router and say
Ø  Router(config)# router eigrp 1
And then go to another router and say
Ø  Router(config)#router eigrp 2
Because those are different AS, they would not form a neighborship
                       Something else to matchup is Mismatched K Values do you remember, how the K values influence the Metric Calculation for EIGRP, by default EIGRP only considers bandwidth and delay in its Calculation but we can make EIGRP Consider other things, we can make it consider Reliability and Load through the Manipulation of these K Values and K Values must match between neighbors, lets gets some practice with the EIGRP Troubleshooting by going out to interface
                           In this topology i got all 4 of these Routers configured as EIGRP speaking Routers however, things are not working as anticipated, i am not forming any neighborship let’s see if we troubleshoot and resolve this on Router R1 let’s take a look our 3 EIGRP Tables, i can do a
Ø R1#show ip eigrp topology
                       This can give us a list of networks known to EIGRP and i do know about some networks, these are all locally attached to this Router, we have not learned anything via EIGRP
Ø R1#show ip eigrp neighbors
                 And this does not look good, we don’t have any neighbors and we see that our AS Number is 1
Ø  R1#show ip eigrp interfaces
                           And it’s shows that interface fastetherent 0/1 is participating and you take a look at topology, you see that we have got network of 192.168.1.0/24 connected to fastetherent 0/0, is that interface is not participating in EIGRP or we not gonna be advertising that Network, let’s check that
Ø  R1#show ip protocols
We can see that we are Routing for
ü  10.1.1.1/32
ü  192.168.1.0
ü  192.168.2.0
                        Now i am gonna go over Router 2 and give some command there as well, and let’s see if we can determine why we are not establishing the neighborship between R1 and R2, you wanna may stop for movement to take a look at output that we have on picture and remember some of the things we talk about few movements ago that need to be matchup between Routers for them to become neighbors, let’s go to Router R2
Ø  R2#show ip eigrp interface
                     It looks like all of our interfaces are participating and we can see that our AS number 1 matches up that’s good
Ø  R2#show ip eigrp topology
Don’t see anything that’s not local to me that i have learned
Ø  R2#show ip eigrp neighbors
We don’t have any neighbor
Ø  R2#show ip protocols


                            Did you notice anything that not matching up that needs to match up in order for neighborship to form, we already said that we using the same AS number 1 so, that’s good but did you notice the K Values are just the 1 little bit different the K Values which we can change how the metric is calculated, here on R1 the K Values are 1 0 1 0 1 and on R2 1 0 1 0 0, the K5 Value on R1 is different, let’s fix that
Ø  R1(config)#router eigrp 1
Ø  R1(config-router)#metric weights 0 1 0 1 0 0
                 And the first Value is a TOS Value, the Quality of Service marking and it’s gonna be 0 then we start putting our Values K1 K2 K3 K4 K5, let’s see if we now have
Ø  R1#show ip eigrp neighbors
Great news! We are now neighbor with Router R2, let’s check if learned anything
Ø  R1#show ip eigrp topology
We have learned about 172.16.0.0/16 network via EIGRP
Ø  R1#show ip route
                  D- indicates EIGRP and we can see that EIGRP has an administrative distance of 90 and 2172416 Feasible Distance to get there.
Ø  R1#show ip eigrp topology
Ø  2172416: - in our topology table this is our Feasible Distance or FD this is the metric first to get to this network.
Ø  2169856: - Sometimes called the Reported Distance or Advertised Distance, this is the distance or metric that our neighbor is reporting to us if our neighbor is R2, R2 is saying “here is the distance from me to get to this network
                                        Well we got a neighborship with R2 but still didn’t see whole lots of routes as looking on IP Routing Table, let’s go to R2 to see what neighbors is it knows about
R2#show ip eigrp neighbors

                     We have only 1 formed neighborship with R1, let’s see why we don’t have neighborship with R3
Ø  R2#show ip protocols
We are routing for R3 (172.16.1.0/30), let’s go to R3
Ø  R3#show ip eigrp interfaces
Interface serial 1/0 which gets up to R2 is not participating in EIGRP
Ø  R3#show ip protocols
                  It says we are routing for 172.16.1.0/30, we are Routing for that network but that interface is not participating
Ø  R3#show ip interface brief
             And we are in the UP/UP state, take a movement and look at the output on picture and see if you can find something that might be preventing this neighborship forming

                     Did you notice the IP Address of this interface it looks like incorrect, according to our topology the IP address for this interface should be 172.16.1.2 but now it’s 172.16.2.1, we have wrong ip address, lets fix that
Ø  R3(config)#interface serial 1/0
Ø  R3(config-if)#ip address 172.16.1.2 255.255.255.252
Now just take a look at
Ø  R4#show ip eigrp interfaces
                  We have all interfaces participating but i still have an issue with R4 neither R2 nor R3 has formed a neighborship with R4, what’s going on there, let’s go to R4
Ø  R4#show ip eigrp neighbors
We don’t have any neighbors
Ø  R4#show ip protocols
Notice it says i am routing for 0.0.0.0, do we have an incorrect network statement
                                NO remember the network statement is often misunderstood, the network statement is not saying “Advertise this network via EIGRP”, the network statement is saying “any interface that has an IP Address that belongs to this scope of addresses, defined by the network statement to make that interface participate in EIGRPwe are not saying advertise this network, we saying any interface who’s IP Address belongs to this address space, make that interface participate and i want any all of my interface to participate in EIGRP a shortcut is to say
Network 0.0.0.0, that’s all we done here, take a look at the output

                  Did you notice that we got something major that mismatch between Router 4 and everyone else, Router 4 is in AS 100 everybody else is in AS 1, that would certainly do an issue lets fix that?
Ø  R4(config)#nor router eigrp 100
Ø  R4(config)#router eigrp 1
Ø  R4(config-router)#network 0.0.0.0
Let’s do a
Ø  R4#show ip eigrp neighbors
Ø  R4#how ip route

Now we learned several routes via EIGRP
                      Now that was a look at IPv4 its really similar for IPv6, you notice on topology i have got some IPv6 addresses configured, let’s make sure that context of these databases of IPv6
Ø  R4#show ipv6 eigrp interfaces
Ø  R4#show ipv6 eigrp topology
Ø  R4#show ipv6 eigrp neighbors
                           That’s the look at some of really common reason why a neighborship might not be forming with EIGRP and our next session we gonna take a look at anther common EIGRP Troubleshooting targets and that is some of my Routes not showing up, i am not able to learn all of the networks that i think should be learn via EIGRP.


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1 comment:

  1. Great Article
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