[c-nsp] Failover with 3550-SMI

[Brian Turnbow]

Ther ewas a discussion not to long ago on this list about using private ip address between routers for running HSRP, take a look in the archives. Basically the HSRP'd address is the public IP used as the default and the 2 router (or switches) use private ip's to communicate. That way you don't waste space. 
As for the solutions 1 and 2 give you full redundancy whereas with number 3 the router becomes your single point of failure.
The 3550's only support 16 HSRP groups so be carefull if you need more the 3750s will do more (32 I think) 

Brian

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Marco Matarazzo
Sent: giovedì 25 novembre 2004 15.19
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Failover with 3550-SMI

Hi all,

I manage a colo-like network, quite simple:

Two borders (7206/NPE400/256Mb) each talking eBGP with two upstreams (double feed each upstream) and iBGP between them.
Those two 7206 trunk each into a different 2950T-24, that are also connected together. Then finally a couple of 3550-48-SMI, each connected with both switches, that talk RIPv2 with the borders (they announce the connected routes, and take the default gw from the borders). All the ports are layer3 (except the links to the switches that are layer2, configured for spanning tree).
In this setup I can only see the 3550 as Single Points of Failure.
Now some customers want dual ethernet for failover. I can see three
scenarios:

1) Put them on the two 3550 layer2 ports, and route the vlan directly on the border, using HSRP on the border for default gateway failover.
2) Upgrade the 3550-SMI to EMI, and run HSRP between the two customers facing interfaces.
3) Don't upgrade the 3550, add little router to the customer and advertise the default route to this router via RIP.

Is there something I overlooked? Could I use some other failover method?
Which of the three would you use? I prefer the third solution, as it keeps the border and the distribution completely separated, and it seems more manageable. But that's also the most waste of IP space (need two additionals /30). Number 1 could also be feasible, but if number of customers wanting dual ethernet rises, I think that 30 or 40 HSRP istances together with two full BGP feeds and three downstreams, netflow, RIP and some access-lists could kill the router (transit traffic is 40Mbps, router is as 25/30% CPU).
Number 2 is expensive (the upgrade to smi to emi), and again, could theorically a 3550 handle 48 HSRP instances easily?

Thanks!
]\/[arco

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