[nsp] Cat6509/MSFC2 hybrid, hw switched multicast forwarding freezes

Matti Saarinen mjs at cc.tut.fi
Fri Aug 22 12:04:21 EDT 2003

     Now, I've got this issue solved.

> I found out the forwarding of the multicast stops at the moment when
> a new hardware switched flow for the host that has joined to the
> group is installed

     In the box suffering from this problem, there is a long access
     list applied the interface though which all the external
     multicast traffic arrives. The TAC engineer investigating the
     case found out that the long access list somehow messed up the
     MMLS tables. That resulted in the state where the amount of free
     memory was too low and the hardware switched multicast didn't

     The solution was to change the algorithm the MSFC uses for
     merging the ACL entries to TCAM (The IOS command is mls aclmerge
     algorithm [bdd|odm]). The default algorithm in IOS was BDD and
     the one we are using now is ODM. The algorithms itself are
     described in the following web page if someone is interested:


     When I modified the long ACL the switch did produce a log message
     referring to TCAM and ACLs. Still, I wasn't able to conclude the
     connection between the trouble with multicast and the TCAM. 

- Matti -

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