[c-nsp] problems migrating to a 3550

Andy Dills andy at xecu.net
Wed Feb 3 10:39:46 EST 2010

I'm migrating a network from an old HP Procurve switch to a Cisco 3550. 

Simple setup, public and private vlans. Setup a port to be tagged on both 
vlans on the HP side, and on the cisco end set it to be in trunking mode. 
The cisco sees the vlans. I'm getting the full table from 'show mac 
address-table', with the appropriate vlans attached to the appropriate mac 

Things in vlan2 on the HP switch can reach the IP address of the 3550 on 
vlan2 just fine, vlan2 is solid. 

However, things in vlan1 on the HP switch cannot reach the IP of the 3550 
on vlan1, and anything attached to 3550 on vlan1 ports cannot reach 
anything on vlan1 on the HP switch.

Both switches have all of the correct mac addresses in their layer 2 
forwarding table. However, whereas things on vlan2 are consistently 
reachable and populate the arp table, on vlan1 some things will show up in 
the arp table, most will not, and none will be pingable.

Another symptom I'm noticing is that nothing on vlan1 on the HP switch can 
see the mac address for the vlan1 interface on the 3550, or of anything 
attached to vlan1 of the 3550. However, these mac addresses will be in 
both switches forwarding tables. And likewise, there will be addresses in 
the forwarding table of the 3550, but somehow the server is unable to get 
arp resolution for any of those very hosts.


interface FastEthernet0/48
 switchport trunk encapsulation dot1q
 switchport trunk allowed vlan 1,2
 switchport mode trunk

interface Vlan1
 description Public
 ip address
interface Vlan2
 description Private
 ip address
ip route

public#sh interfaces trunk 

Port        Mode             Encapsulation  Status        Native vlan
Fa0/48      on               802.1q         trunking      1

Port        Vlans allowed on trunk
Fa0/48      1-2

Port        Vlans allowed and active in management domain
Fa0/48      1-2

Port        Vlans in spanning tree forwarding state and not pruned
Fa0/48      1-2

Running Version 12.2(44)SE6.

Any suggestions?


Andy Dills
Xecunet, Inc.

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