eigrp routes disappearing

[robdog01]

Hi everyone,

Does anyone know why when there are no host devices connected to a particular vlan on switch a, that the eigrp routes on switch b, c, d, etc.. disappears?

for example, on switch a:

vlan 100

ip address 172.16.1.1 255.255.255.0

no shut

vlan 200

ip address 10.10.0.1 255.255.255.0

no shut

if there are no host devices on vlan 100 on switch a, then there are no eigrp routes on the other switches to 172.16.1.0 /24.

Does anyone know how to persist the route to 172.16.1.0/24 even if there are no devices connected?

Thank you!

[ankbhasi · Accepted solution]

Hi Rob,

You need to have atleast one active physical interface for a vlan to make its layer 3 interface up and up and if there are no active device the logical interface will stay down and is the reason for your problem.

I belive the workaround will be to have a trunk link on a switch carrying those vlans so that the logical interface stays up all the time.

HTH

Ankur

[robdog01]

Thanks for the quick response..

I read somewhere about using loopback interfaces for routing protocols.. do you think that would help in this case?

Thank you.

[sundar.palaniappan · Accepted solution]

Rob,

Though, both loopback & VLAN interfaces are virtual they differ somewhat in how they operate. Loopback interfaces never go down. VLAN interfaces, on the other hand, would go down if there are no active ports on that VLAN or an active trunk in which that VLAN is active.

AFAIK, there's no way to keep the VLAN interfaces up when the above conditions aren't met. Even, if you configured a permanent static route on the adjacent switches for those VLANs it wouldn't serve any purpose as the VLAN interfaces wouldn't be up anyway.

HTH

Sundar