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HSRP using VLAN with different network subnet masks

I have configured a few VLANs uplinked to 2 x 4506 L2/L3 devices. All VLANs,

except one, is a different 10.1.n.n/24 network and the 4506's are configured for HSRP for each VLAN. ( .1 virtual, .2, .3). As well, OSFP has the 10.1.0.0 network defined.

HSRP tests between the VLANs using SHUTDOWN worked well.

Then I added a 159.128.208.0/21 VLAN to the configuration. HSRP was defined on the 2x4506 switches as for teh other VLANs. The VLAN was not added to OSPF.

Connectivity to/from these two network groups was confirmed.

However, HSRP tests were strange. If the ping is sent from 159.128.208.0 to a device on any 10.1.0.0 VLAN and the active 10.1.0.0 or 159.128.208.0 router interface is shutdown, recovery either does not happen at all, or every second ping times out.

??????

Is there a problem with OSPG and HSRP together?

Should I add this new network to OSPF?

2 REPLIES
Bronze

Re: HSRP using VLAN with different network subnet masks

At the first look, it looks really strange but What i can visualize is that your ping requests are reaching your destination but the replies somehow come in two direction (May be the routing table has 2 paths for the return path) and one of the reply dont reach ping originator because one of the HSRP interface is shutdown.

I would better check the routing table for any multiple paths in both directions

Bronze

Re: HSRP using VLAN with different network subnet masks

Indeed without more info on the topology I would guess that (some of) the return traffic ends up on the switch where the vlan interface is shutdown and this switch does not have a route to 159.128.208.0.

Possible solutions:

- add 159.128.208.0 to ospf (and use passive-interface if you do not want to route over this vlan)

- redistribute connected in ospf

- add a static route to 159.128.208.0 via the other switch (it will be overridden by the connected route as long as the vlan interface is up)

hth

Herbert

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