[c-nsp] intra-chassis stacking

[Seth Mattinen]

Joe Abley wrote:
> Hi all,
> 
> I am puzzling over a cisco 2851 which has both a HWIC-D-9ESW 9-port  
> switch module and a NM-16ESW-1GIG 16+1 port switch module.
> 
> The switch modules do not seem to be behaving as I would expect. ARPs  
> are succeeding and failing apparently at random, OSPF adjacencies are  
> not forming, and general layer-2 badness abounds.
> 
> The small amounts of cisco docs available about this configuration  
> suggest that "intra-chassis stacking" must be configured, but details  
> on exactly what that means are a little light. The best indication I  
> have seen suggests that I need to insert a crossover cable between  
> the optional gigabit modules on each of the cards; however, it  
> doesn't seem like gigabit ports are an option on the 9-port HWIC, and  
> the gig port on the 16+1-port NM is already in use.
> 
> I have no requirement for VLANs to span the two modules -- I can  
> easily keep all the ports on the 9-port HWIC in a single VLAN, and  
> not expect any ports in the 16+1-port NM to join those VLANs.
> 
> Any suggestions as to whether this configuration can be made to work  
> in a sane way?
> 

As far as I know, the 2800's don't bridge L2 traffic between switch 
modules internally and the "stacking" has to be done with an external 
cable between one port on each. Treat them as two physically separate 
switches, not as one 25 port switch.

~Seth