Hi Every body!
Let say we have two L3-switch, sw1 and sw2
Both sw1 and sw2 have one vlan i.e vlan 1, both switches are connected by access link f0/2 which is also in vlan 1
sw1 0/2-------------------- 0/2 sw2
interface vlan 1
ip address 188.8.131.52/24
sw2: interface vlan 1
ip address 184.108.40.206/24
Will sw1 and sw2 exchange routing updates on f0/2? If f0/2 were trunk, would the updates still be exchanged? if there is another access link also in vlan 1, connected to another switch , will the routing updates be sent on that link?
Thanks a lot!
the answers are :
a) Will sw1 and sw2 exchange routing updates on f0/2?
yes if there was another subnet to advertise (see Rick's post), the ports are in STP forwarding state and allow to: have the SVIs up/up (autostate).
The RIP advertisements are multicast frames if RIPv2 or broadcast frames if RIPv1.
b) If f0/2 were trunk, would the updates still be exchanged?
yes if there isn't a native vlan mismatch (if the trunk is 802.1Q with ISL this can never happen)and vlan1 is not denied on the trunk (actually this on some IOS switches cannot happen: I see vlan1 in the list of permitted vlans even if I've given the list of vlans as 5,6,7 for example)
to consider the SVI up/up also a trunk port can be considered as a port in vlan 1 and in STP forwarding state.
This is important in some scenarios.
c) if there is another access link also in vlan 1, connected to another switch , will the routing updates be sent on that link?
yes because the RIP advertisements are multicast frames if RIPv2 or broadcast frames if RIPv1.
So they are sent out every L2 switchport that is an access port of vlan1 or it is a trunk port carrying vlan1.
This the advantage of using SVIs instead of routed ports they use the L2 switch topology. (and part of the drawbacks too)
Rick has pointed correctly that RIP is missing the neighbor state machine concept: it sends updates only if there is another subnet to announce.
There was another thread about this of someone that was doing tests and he couldn't see routing updates for the same reason.
Hope to help
No routing updates will be exchanged in the situation that you describe. The switches only know 1 network/1 subnet and so they have nothing to advertise. If you were to run debug for rip you would see that rip goes through its periodic process of building routing updates and then determines that it has nothing to advertise over the interface and nothing is sent.
Note that if the routing protocol were OSPF or EIGRP instead of RIP that the routing protocol hello messages would be sent over the link, but again no routing updates.