[nsp] Routing through Management Vlan on 3750?

[Deepak Jain]

I know I'm replying to my post, but since these things seem to have a 
long shelf life in google....

I opened a TAC ticket on this issue, and it looks like the 3750 might 
have some problem with caching on these interfaces. The packet loss and 
problem disappeared once caching was turned off. YMMV.

DJ

Deepak Jain wrote:

> 
> On a 3750,
> 
> g1/0/24 - g1/0/27 are L2 ports that bring traffic into the box over VLAN 1.
> 
> g1/0/28 is the uplink (no switchport, ip addr x.x.x.x)
> 
> There is a default route to the uplink on g1/0/28.
> 
> int vlan 1
> has several ip addresses configured corresponding to all of the networks 
> on g1/0/24-g1/0/27.
> 
> For numerous legacy reasons, the address allocations and port 
> allocations don't easily correspond to discrete subnet masks.
> 
> No ip addresses are configured on loopback 0 or anywhere else.
> 
> Pinging/tracing from the 3750 to the rest of the internet is fine.
> 
> Pinging from the 3750 to any of the hosts on g1/0/24 - g1/0/27 seems 
> fine, at HIGH packet rates, some packet loss is noted -- could be the 
> server or it could be the config. But it leads to the question:
> 
> Is there a performance limitation on this configuration (by requiring 
> VLAN 1 to do all of the routing between the interfaces and the rest of 
> the internet). Peak aggregate traffic is > 1000Mb/s, typical traffic is 
> around 300Mb/s right now.
> 
> There is a strange problem that appears occassionally, and is not 
> predictable. The problem is the hosts are not able to trace through the 
> router. Traces show the router IP at hop 1, and then stars from there 
> onwards. Traces in from the internet work fine all the way to the host. 
> TCP connections (telnet to the host) do not even connect, but work fine 
> from the CPE router. This obviously causes the bulk of the problems.
> 
> I am _wondering_ if this is a broadcast problem as broadcasts might not 
> be being re-sent down each interface, and since there is the legacy 
> problem with the addressing, a simple broadcast helper might not cut it.
> 
> I don't want to configure a bridge group because the total traffic 
> exceeds a single link, and Etherchannel doesn't work because each port 
> goes to a different aggregation switch.
> 
> My understanding is that this configuration should work, while being 
> less than optimal. Further, the configuration did work, but has recently 
> begun showing issues for the customer, possibly correlating to an 
> increase in traffic flows around the Holiday season.
> 
> Is there a big difference between VLAN 1 and one of the others? The 
> example I saw on the Cisco web site showed VLAN 1 being disabled, so I 
> don't know if the solution is that simple or its something more 
> problematic.
> 
> Thanks in advance,
> 
> DJ
> 
> 
> 
> 
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