[nsp] Routing through Management Vlan on 3750?

[Jeff Nelson]

I appreciate you following up on your own post. I've been looking to use the 3750 for some one-off scenarios and with every new device comes some new "features". I'll file this one.

--jeff
Deepak Jain(deepak at ai.net)@03/12/16 23:27:
> 
> 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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> >
> >
> 
> 
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-- 
Jeff Nelson
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