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New Member

CSS arp cache limit

I am looking at deploying 2 x CSS11503 (inline redundant) in an environment where it may have to statically route for a large number of hosts. The largest network any interface is directly connected to is a /24, but static routes on the CSS may be needed for up to 32 x /24s. I am interested to know if the requirement to statically route for up to 8192 hosts could max out the arp cache, which I believe is limited to 5k.

Thanks - mike

Cisco Employee

Re: CSS arp cache limit


you will definitely hit a limit here.

Also, I don't see why you can't create summary route ?

How many interfaces do you have on your CSS ?


New Member

Re: CSS arp cache limit

Thanks Gilles

4 interfaces on the CSS

Summary route - unfortunately not - the /24s we statically route to are distributed in a non-contiguous manner across 6 gateways (this is flagged for change, but not in the timescale we have)

As all statically routed networks (and 95% of hosts)are one or more hops away, I was thinking it would only be directly attached networks with arp entries?

Is this not the case?


Cisco Employee

Re: CSS arp cache limit

I'm really concerned about the size of the routing table.

Even on a router I would be concerned.

The CSS has a strange way of combining routing table and arp table that was inherited from the past when the company was acquired.

We never tested the CSS with such a high amount of routes [static or dynamic].

Therefore I would suggest you to find a way to reduce this routing table to 1000 routes.


New Member

Re: CSS arp cache limit

Sorry Gilles - I misunderstood - the routing can be done at the /24 to /28 level - we should only have a couple of hundred routes at the most.

Our main concern is confirming that it will only be the directly attached networks that will have an arp cache entry.


Cisco Employee

Re: CSS arp cache limit

2-3 hundreds routes is ok. No worries.


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