Bridging vlans without forwarding packets

[Marinache Andrei]

Hi!

I have the infrastructure in the attached image:

Location B, with cisco 2950 and 2970, with layer2 links from two providers.

Location A, with cisco 2970 and 2x7301 routers, that should be configured in HSRP mode.

Provider A transports vlans 10 and 20 from location B to location A

Provider B transports vlans 10 and 20 through its MPLS networks and these vlans get to location A as vlans 40 and 50 (vl40=vl10; vl50=vl20)

None of the providers can forward BPDUs in their networks.

What I need is a way of automatic failover in case that one of the links is down (not forwarding traffic, even if the link is physically up)

Thank you!

[Giuseppe Larosa]

Hello Andrei,

some form of falloever bridging might be supported on the C2970, but not for IPv4 traffic.

I cannot find a config guide for C2970, but the cfg guide for C2960 does not mention bridging between vlans

see

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/15-2_2_e/configuration/guide/b_1522e_2960_2960c_2960s_2960sf_2960p_cg.html

My suggestion is to create a single domain VL10-VL40 using two ports one access port in vlan 10 and one access port in vlan40, connect them with a LAN cable.

Do the same for VL20-VL50, use another pair of access ports one is placed in vlan20 and the other in vlan50.

The trick works because Cisco switches send IEEE version of STP BPDUs on access ports so they do not detect the different Vlan-id at the two ends.

CDP can detect the native vlan mismatch, but you can disable it on the ports involved in merging the Vlans.

This is a poor man solution, but given your hardware I'm afraid it is the only viable choice.

Hope to help

Giuseppe

[Marinache Andrei]

Uplinks from site A to site B can't transport BPDUs.

In site B I don't need to change or bridge VLANs, only in site A where i have the 7301s.

I think i've found a way of doing it with sla and scripts (moving the gateway IP), but maybe there's a better way.