EIGRP over trunks

[Mokhalil82]

Hi

I need to form an EIGRP neighbor relationship between 2 x 3750 switches but they have 2 x 2960 layer 2 switches sitting in between them.

The layout is as follows.

3750---------------2960---------------2960--------------------3750

How would this be possible. Can the eigrp pass over these trunks through a vlan.

Any help will be much appreciated

Thanks

[Peter Paluch]

Hi,

How would this be possible. Can the eigrp pass over these trunks through a vlan.

Yes, absolutely. EIGRP is a protocol whose messages are encapsulated in IP packets. If there is an IP connectivity between the 3750 switches, EIGRP will run perfectly. How are you going to configure the 3750 - are you going to configure an interface Vlan with an IP address and run EIGRP on this interface, or are you going to configure routed ports from 3750 toward the 2960?

Best regards,
Peter

[Mokhalil82]

Thanks for the response. There are already vlans running over this trunk link so I want to create vlan interfaces on each end on the 3750's. I have setup EIGRP before but not when using Vlan interfaces.

Would the eigrp config be done in global config mode or on the vlan interfaces?

[Kevin Santillan]

Assuming IPv4, you'll need to enable it globally on each switch and define a network statement that would match the SVI's address.

Ex:

router eigrp 1

network <SVI address> 0.0.0.0

[Gertjan Fober]

Hi just an other question on this topic. What if there would be 2 VLANs on that trunk dat use separate EIGRP groups.
Lets say VLAN10 is advertised in EIGRP 1 and VLAN 20 is in group 2. Would that be a propper way of segmenting?
 

[Peter Paluch]

Hello,

Lets say VLAN10 is advertised in EIGRP 1 and VLAN 20 is in group 2. Would that be a propper way of segmenting?

That would depend on what your requirements are. Keep two facts in mind: First, VLANs indeed separate hosts into standalone and isolated broadcast domains, but if there is a router that connects to all VLANs and each of them uses a unique IP subnet, then hosts in these VLANs can possibly communicate through the router with each other. In other words, VLANs are used to work with groups of hosts more efficiently, but they are not intended to prevent them from ever communicating to each other. Second, if two independent EIGRP processes are started on a router or a multilayer switch, they will not share any routing information unless explicitly configured to do so.

Now, if VLAN10 was advertised in EIGRP 1 and VLAN20 in EIGRP 2, then all routers running EIGRP 2 would be missing the IP subnet used in VLAN10, and vice versa, all routers running EIGRP 1 would be missing the IP subnet used in VLAN20. Consequently, hosts in VLAN10 would be unable to speak to anyone whose address is carried in EIGRP 2 (because they would not see the network in VLAN10 and would be unable to respond back), and similarly, hosts in VLAN20 would be unable to speak to anyone whose address is carried in EIGRP 1. As I indicated earlier, this may or may not be what you want to achieve.

Feel welcome to ask further!

Best regards,
Peter

[Gertjan Fober]

Hi Peter,

Thanks for your reply. This is indeed what i would like to achieve.

I read in the requirements that the interface is actually advertised in the group due the subnet you enter. I thought that using the same interface with different subnets could cause problems when not correctly filtered.

Though if i understand you correct this is not the cause and when the subnets are not in the same EIGRP group they cannot communicate between each other? I want to use the same connection for networks that will not share traffic except the ones in the same EIGRP group.

Thanks in advance!

Regards,

Gertjan

[Peter Paluch]

Hi Gertjan,

Can you give me an example with actual addresses please, including a description of what should be accomplished? I am somewhat lost in trying to understand how your scenario is going to look like - it's just my daftness so please bear with me :)

Best regards,
Peter

[Gertjan Fober]

Hi Peter,

My appologies for the late reply and no problem.
VLAN 10 and 20 are only used for making the connections. they are actually an external L2 network. What i like to do is start with segementing the networks in the EIGRP groups but sometimes the same lines are used for the traffic.

Hope this clarifies what im trying to achieve.

[Masoud Pourshabanian]

EIGRP is a layer 3 protocol. Your 2960 passes EIGRP messages without having any idea about them.

As long as, your 3750 switches see each other, you do not have to be concern about 2960.

Sample

Make trunk interfaces between two 3750 and 2960 , then create interface vlans on your 3750

3750-1

Int vlan 10

192.168.1.1 250.255.255.0

**************************************

3750-2

Int vlan 10

192.168.1.2 250.255.255.0

Now 3750-1 can see 3750-2  Then

************************************************

3750-1 and-3750-2

Router EIGRP 1

network 192.168.1.0 255.255.255.0

Add your other networks here

Just make sure to create vlan 10 in both 2960 switches

Hope it helps,

Masoud