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PSA: Global IPv4 Routing Table Hits 500k Routes

By stretch | Tuesday, May 6, 2014 at 10:01 p.m. UTC

Last week, the global IPv4 routing table has surpassed the 500 thousand route benchmark, according to the CIDR Report. The graph below shows its progression since the early nineties:


I last wrote about global IPv4 growth in August of 2009, when the table size was at a mere 300 thousand routes. While that benchmark was largely ceremonial, this one crosses a threshold which should may be of grave concern for many.

As has been pointed out on the NANOG mailing list, we are quickly approaching the hard forwarding plane capacity limits which exists on several very popular platforms, namely the Cisco 7600/6500 and RSP720/Sup720. The default TCAM partitioning scheme of these platforms allows for a maximum of 512 thousand IPv4 routes.

If you accept full Internet routes anywhere on your network, you'll want to verify the maximum table sizes for those platforms. On the 6500/7600 platform, the current partitioning scheme can be inspected with show mls cef maximum-routes:

Router# show mls cef maximum-routes
FIB TCAM maximum routes :
Current :
 IPv4 + MPLS         - 512k (default)
 IPv6 + IP Multicast - 256k (default)

The good news is that it's easy to repartition the default scheme (e.g. mls cef maximum-routes ip 768) to allow for more IPv4 space. Unfortunately, this requires taking the device out of production for a time to be rebooted.

Thanks to @nixgeek and the NANOG folks for inspiring this post!

Posted in News


Pete Lumbis
May 6, 2014 at 10:51 p.m. UTC

If you have an ASR9k with a Trident based card the guide on how to adjust the default table sizes can be found here.

May 12, 2014 at 8:58 a.m. UTC

Is there any other requirement (DRAM capacity..) to be fulfilled before increasing ipv4 space on Cisco 6500 Sup7203BXL? Thanks

Maxim B.
May 19, 2014 at 2:54 p.m. UTC

What about 7200 platform? Is it affected?

June 17, 2014 at 4:34 p.m. UTC

While you can use "show mls cef maximum-routes" to see the maximum you are configured for you can use the following command to find out where exactly your TCAM usage is at on the 6500/7600 "show platform hardware capacity"

July 10, 2014 at 10:54 p.m. UTC

Wondering about using a 3900 series router with multiple VRF's having full internet tables. Anyone know the commands on the 9G series to see max capacity or the correct Cisco documentation. I'm still searching for it on Google/Cisco.

John Thorpe
August 14, 2014 at 9:30 p.m. UTC

So in about 6 years we hit 768k, what are you going to do then?

September 25, 2014 at 9:32 p.m. UTC

@John..unless you're running SUP2T versions of these platforms, by that time you will need to swap them for ASR9k boxes anyway as they will be out of support (believe the 720s are somewhere in 2018). By then, most probably the 9k Trident line cards will be phased out so you will be going for Typhoon cards (or newer models) which shoots your scalability in excess of 4 million routes (depending on your IPv4/v6 table combinations).

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