TCAM behaviour

[Isenau]

Hi,

I'm trying to troubleshoot some connectivity issues and in the process of collecting some reference data I noticed some strange TCAM behaviour. When the network is ok we see this:

Code: Select all

switch01#show platform hardware capacity pfc

L3 Forwarding Resources
             FIB TCAM usage:                     Total        Used       %Used
                  72 bits (IPv4, MPLS, EoM)     196608       17717          9%
                 144 bits (IP mcast, IPv6)       32768           8          1%

                     detail:      Protocol                    Used       %Used
                                  IPv4                       10304          5%
                                  MPLS                        7412          4%
                                  EoM                            1          1%

                                  IPv6                           1          1%
                                  IPv4 mcast                     4          1%
                                  IPv6 mcast                     3          1%

            Adjacency usage:                     Total        Used       %Used
                                               1048576       17285          2%

but when there are issues we see this:

Code: Select all

switch01#show platform hardware capacity pfc

L3 Forwarding Resources
             FIB TCAM usage:                     Total        Used       %Used
                  72 bits (IPv4, MPLS, EoM)     196608      196147        100%
                 144 bits (IP mcast, IPv6)       32768           8          1%

                     detail:      Protocol                    Used       %Used
                                  IPv4                        5103          3%
                                  MPLS                      191043         97%
                                  EoM                            1          1%

                                  IPv6                           1          1%
                                  IPv4 mcast                     4          1%
                                  IPv6 mcast                     3          1%

            Adjacency usage:                     Total        Used       %Used
                                               1048576       17593          2%

has anyone seen this kind of behaviour before? When there are issues about half the eBGP sessions go down (so I can understand the IPv4 TCAM utilisation dropping) but why the leap in MPLS utilisation?

thanks.

[Ivan Pepelnjak]

Some MPLS thingie is going crazy. What are you doing with MPLS on this box?

[Isenau]

Nothing special is done with MPLS - it's standard PE functionality, with no TE or special features enabled. A completely different box crashed this morning with messages about hardware cef entries exceeding capacity for the mpls protocol.

I've opened a tac case, but just wondered if anyone had come across anything like this before? It all seems perfectly fine now...

thanks.

[Ivan Pepelnjak]

A CE router gone crazy and inserting loads of MPLS VPN routes?
Someone somehow dumping the whole Internet into your boxes?

Inspect the LFIB and try to figure out what's eating all those labels.

[Isenau]

Traced to a bug in IOS, but very hard to nail down. A new engineering release seems to have fixed it.