Forming EIGRP Adjacency between two routers connected to a switch

[Frank27]

If I have two routers , both trunking to vlan native 1 to a switch (without router on a stick from the router side)

and I want to create an EIGRP adjacency between these two , is this possible?

[Richard Burts]

Am I correct in understanding that there is a switch with multiple vlans and that the interfaces used to connect to 2 routers are configured as trunks but that the interfaces on the routers are just using the physical interface and no subinterfaces? In that case the routers should be able to form EIGRP neighbor adjacency. The routers would route packets from that vlan but would not route anything for the other vlans on the switch.

You ask if EIGRP adjacency is possible and the answer is yes. But I am puzzled why you would have a trunk with multiple vlans and only route for one of the vlans.

[Frank27]

yes correct. i this is an internal native that i use for a DMZ area.

But no adjacency so far.

I also compared the metric and is just the same.

R1>router eigrp 10

R1>network  192.168.0.0. 0.0.0.255 

R2> router eigrp 10

R2>network 10.0.0.0 0.0.0.255 

both /24 mask

[Jon Marshall]

Is that your full EIGRP configuration ? 

If so that won't work ie. you need a common subnet between the routers. 

Jon

[Frank27]

solved through RIPv2.. still  i am troubleshooting the issue , but thanks for your suggestions.

[MHM Cisco World]

without router in stick? how you config the link between the R and SW.

[Martin L]

In order for 2 routers to establish adjacency and exchange routes they must be on the same subnet; aka common subnet or link. They usually are also directly connected (via L2 switch or back-to-back/crossover cable) but not via another L3 device; exception is BGP.  

Regards, ML
**Please Rate All Helpful Responses **

[Richard Burts]

The original poster tells us "still i am troubleshooting the issue" I am not clear what there is to troubleshoot. It is now clear that R1 is in one network and R2 is in a different network. So apparently there is a single vlan with 2 networks implemented in it. (which is a possible but very unusual situation)

Some routing protocols (like EIGRP and OSPF) have the concept of establishing neighbor relationships and then advertising using those neighbor relationships. Since the 2 routers are in different networks attempts to form a neighbor relationship fail. And those protocols do not allow these routers to communicate. RIP does not have a concept of neighbor and just sends out its routing update. This does allow the 2 routers in different networks to communicate.

[Frank27]

Sorry I see a bit of confusion and partially is made by previous explanations .

R1 and R2 are on the same subnet and VLAN .

R1 is sharing GE0/0 physical interface to S1 (switch)

R2 is sharing GE0/0 physical interface to S1 

They both are under the network 192.168.0.0/24 

R2 has another interface , connected to another network. Let's say 10.0.0.0/24

I want to advertise the 10.0.0.0/24 to R1.

If using RIP it works. If using EIGRP doesn't.

About the common VLAN -- this is just a testing lab (with physical equipment). 

The VLAN on the switch as I said is representing a DMZ since other VLAN are passing through an ASA connected to the same switch.

[paul driver]

Hello

R2 has another interface , connected to another network. Let's say 10.0.0.0/24

I want to advertise the 10.0.0.0/24 to R1.

you shouldn’t have to use rip to have that other network advertised into eigrp- just a simple network command in the eigrp routing process should do it as both of those networks are directly connected to R2 which has a eigrp adjacency to R1 but you are saying it’s not being advertised correct ?- do you have auto-summarisation turned off it should be but just check.

sh ip protocols 

[Richard Burts]

We do not have enough details about this environment to understand the issue or to give good advice. To help us would you provide the output of these commands on both routers:

show ip interface brief
show run | section eigrp
show ip eigrp interface
show ip route

There is some mention about using switch as DMZ. Could you provide some details about how the switch is configured.