Collapsed core, full mesh - redundancy L2 or L3?

[vpmorozov]

Hi, people!

What is the best legacy solution for redundancy in that case:

I've a collapsed core with four Layer-3 switches and full mesh between them. Every switch has 5-10 /24 networks behind them.

There are 2 solutions to provide redundancy between core switches:

a) Make 1 VLAN between all of them and implement RSTP;

b) Make 6 VLAN (one between every pair) and implement routing.

I'm going to b), but may be someone have something to say :-)

Thanks a lot!

[sachinraja]

Hello,

I would also advice for B, just because the network on the Core is really complex. I mean, if you have 4 core & links going everywhere, STP will become a real big mess. I'm sure routing (even though a little more in convergence than RSTP), will give you ease of maintaining/troubleshooting and scalability factors. The only disadv i see with B, is that you cannot extend VLANs between the switches. If this is the business model of your organisation, it is fine to have B as the solution !!!!!

Incase, you had 2 core instead of 4, and you had redundant links to the L2 Edge, with a connectivity back-to-back between the core (standard design), I would look only for RSTP. With traditional STPs like 802.1d, the convergence times were really high (50 secs).. L3 on the trunks, would really make more sense then. but with RSTP, which can give really fast convergence (1 or 2 secs), it can precede over having L3 trunks on your network...

Just to conclude, i would go for Solution B, ONLY IN UR CASE & the important things to consider between L2 or L3 trunks are convergence times, scalability, Ease of management/troubleshooting, VLAN extension, etc etc..

Hope this helps.. all the best.. rate replies if found useful..

Raj

[vpmorozov]

Hi, Raj!

Thanks for reply!

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The only disadv i see with B, is that you cannot extend VLANs between the switches.

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Usually customer don't need one VLAN, but need one IP network in different locations... If topology is complex and end-to-end VLAN is highly undesirable, it's possible to resolve with ProxyARP somehow... I suggest... :-)

But anyway it's not my case now...

Thanks!

Vlad.

[sachinraja]

Vlad,

I was actually not mentioning on the VLAN propagation between different locations , ie on the WAN.. I was more talking about the VLAN dispursion on the Local Building. Say, in case you have your laptop on the 1st floor, on VLAN 3, and you suddenly want to go to 4th floor which is on a totally different VTP domain, you cannot be assigned on the same VLAN 3 & IP address !!!

Anyway, all the very best for your new design and wish you a happy new year !!!

Raj