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Weird issues with routing

benben_3
Occasional Advisor

Weird issues with routing

OK. I'm stumped. It's probably something stupid but here goes...

I have two sites. lets call them site 1 and site 2, at each site I have 2 5300XL running RSTP and XRRP. It's not a complicated setup, the 2 switches are trunked together and edge switches have redundant paths to each switch.

Now, I have a layer 2 connection between the two sites - I created a new vlan dedicated for this, gave IPs to each switch on this vlan and plugged in the layer2 connection. I couldn't ping the switches at the other site, yet I could ping the other switch at the same site.

I noticed that when the layer2 connection was plugged in the two sites started talking RSTP to each other and thus the root switch changed. This might be expected I think this might be causing the issue.

I then went back to basics, and just created the new vlan on one switch at each site (where the layer2 connect plugs in). I still couldn't ping the other IP.

I then decided to investigate ARP on the vlan and on one switch i could see the MAC address/IP of the other but not vice versa. 'show cdp neighbor' shows that they are seeing each other.

Getting frustrated I then took the cable out of the 5300XL at one site and wacked it into a 2600 switch, simple setup with no STP. This worked perfectly.

I don't suppose anyone has any ideas as to what I can investigate next?

Thanks in advance!
6 REPLIES
Mohieddin Kharnoub
Honored Contributor

Re: Weird issues with routing

Hi

Let talk in simple way.

Say we have 2 Switches with multiple Vlans and routing enabled on both,
If we just need a L2 connectivity, then we simply create one Vlan on both Switches and TAG the link between them to this Vlan

And no matter whats the IP you configured on this Vlan on both Switch, if you have one client on both side they should be able to talk.

So be sure you check this on both sites, the Vlan you created (no IP needed unless routing is required to other Vlans) and its Tagged on the Uplink between the 2 Sites.

Regarding the Spanning Tree, you should consider each site has its Own Spanning Tree Topology.

So, on both sites make sure you enable Spanning tree priority 0 on Core1 and Priority 1 on Core2 .

And, enable BPDU protection on the uplink between the 2 sites, so NO Spanning Tree bpdu Chat will happen on that uplink between the 2 sites.

Good Luck !!!
Science for Everyone
benben_3
Occasional Advisor

Re: Weird issues with routing

Thanks for the quick response - the bpdu stuff sounds like what I want as i wish to keep the two STP topologies separate.

Just a quick question, rather than bpdu-protection, do I want to use bpdu-filter as the filter prevents tx and rx of bpdu which of course manipulates the STP topology?

Thanks
Mohieddin Kharnoub
Honored Contributor

Re: Weird issues with routing

Hi

In fact what i meant by bpdu protection is enabling the filter not the protection command

because once you enable bpdu protection, the switch will disable (drop the link) of that port once it receives a spanning tree bpdu
and this port in fact will expect a bpdu from any side.

What you need to enable is the bpdu filtering which will filter the bpdu on that specific port :

Switch(config)#span a1 bpdu-filter

Good Luck !!!
Science for Everyone
benben_3
Occasional Advisor

Re: Weird issues with routing

That BPDU stuff worked a treat - i've now got two separate STP instances.

I'm still having the problem tho, at one site - i can see the MAC address of all the switches on that vlan, however at the other site I can only see the mac of the other core switch (which is trunked) and not the mac addresses of the other switches.

Very strange...

benben_3
Occasional Advisor

Re: Weird issues with routing

After some more investigating, I found get it to work like this...

5300 switch (site 1) subnet A <--> Subnet A 2600 switch (site 1) Subnet B <--> Subnet B 5300 switch (site 2)
benben_3
Occasional Advisor

Re: Weird issues with routing

oops, hit the submit instead of preview button.

With the 2600 routing between the 2 subnets it works fine however I wish to remove the 2600 and just have the 5300's.

sh mac vlan no. shows the mac addreses of the switch at the other site like I said in earlier posts however 'sh arp vlan no.' does now show the IP.

Any further thoughts on this?