[f-nsp] CAM and ip net-aggregate or ip supernet aggregate - does it help to free the cam up ? WAS:AW: cam strangeness
Stephen J. Wilcox
steve at telecomplete.co.uk
Mon Mar 6 16:05:47 EST 2006
On Mon, 6 Mar 2006, Gerald Krause wrote:
> On Monday 06 March 2006 16:48, Gunther Stammwitz wrote:
> > What do the others say: does aggregation help and does the cam
> > usually fill up in an isp enviorment?
>
> I do not use aggregation yet but this might be also interesting: I
> see a lot of /32 CAM entries for destinations that are reachable
> through a supernet which the router learned via OSPF from two neighbors
> via two Ethernet links (= 4 equal paths):
>
>
> (System: NI4GMR/B2P08000)
>
> #sh ip route 212.79.18.100
> Total number of IP routes: 180834
> Destination NetMask Gateway Port Cost Type
> 212.79.0.0 255.255.192.0 212.79.49.135 1/4 20 O
> 212.79.0.0 255.255.192.0 *212.79.49.131 1/4 20 O
> 212.79.0.0 255.255.192.0 212.79.48.3 1/3 20 O
> 212.79.0.0 255.255.192.0 212.79.48.5 1/3 20 O
> #sh cam ip 1/1 | inc 212.79.0.0
> (nothing)
>
> but:
>
> #sh cam ip 1/1 | inc 212.79.18
> 1 8374 212.79.18.198/32 00e0.1e7e.4101 37 1 ether 1/4
> 1 8642 212.79.18.53/32 0050.0b3b.5400 120 1 ether 1/4
> 1 9142 212.79.18.94/32 00e0.1e7e.4101 30 1 ether 1/4
> 1 10131 212.79.18.44/32 0050.0b3b.5470 52 1 ether 1/3
> 1 10601 212.79.18.68/32 00e0.1e7e.4101 7 1 ether 1/4
> 1 11572 212.79.18.100/32 00e0.1e7e.4102 125 1 ether 1/3
>
i dont see this behaviour on both routers with and without aggregation enabled,
i checked against routes learned in ospf with 2 or 3 next hops of the same cost
however i do observe /32s being added where the route is to discard (by having a
static 0.0.0.0/0 to null0) - this may explain why my CAM is getting so full
> Reading the 'Changing CAM Partitions' document on the Foundry website
> does not really enlighten me - especially "Example 2" looks weird for
> me. In my opinion the /32's would make sense for directly connected
> systems or host routes only.... or have I missed something?
yeah i have no idea why they would need to use /32s when simply adding the /30
and not applying aggregation would be better
Steve
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