I have two devices here, a Netscreen SSG520 and a Cisco 3750.
#show ver Cisco IOS Software, C3750 Software (C3750-IPSERVICES-M), Version 12.2(35)SE5, RELEASE SOFTWARE (fc1) Copyright (c) 1986-2007 by Cisco Systems, Inc.
The Cisco is currently being used as the central router. It has an IP interface defined on VLAN1. The revision of IOS is the one recommended to us by Cisco to cover some other oddities we have uncovered in the switch's behavior.
Right now my Netscreen has only an untagged interface. The Cisco treats this as VLAN1, and it works.
I want to add tagged interfaces to the netscreen (I need to remove the Cisco from routing certain VLANs for reasons I won't go into here). So the first thing I do is define the Cisco interface as trunked:
interface GigabitEthernet1/0/1 description Netscreen SSG520 switchport trunk encapsulation dot1q switchport trunk allowed vlan 10,11,102 switchport mode trunk
Now, when I plug in my netscreen, the Cisco reports all the "trunk allowed" VLAN interfaces are UP. It does not report the interface on VLAN1 as up. And the expected traffic does not flow between the Cisco and the Netscreen. Neither can ping the other.
If I plug the Netscreen into an access port defined as so:
interface GigabitEthernet1/0/11 description castor
...the Cisco then reports VLAN1 as up, both devices can ping each other, and traffic can flow between the Cisco and the Netscreen properly.
I have even tried defining the VLANs as tagged sub-interfaces on the Netscreen, and while the tagged VLANs work, VLAN1 does not.
I've played with the
switchport trunk native vlan 1 command and the
no switchport trunk native vlan command and the switch still does not use VLAN1 on that interface.
I already have a
no shutdown command in the definition for interface vlan1; the fact that when the netscreen is plugged into the access port the VLAN comes up proves that.
For various reasons (mostly involving history) we can't just not use VLAN1.
I've spent the last two hours trying to get these devices to talk to each other the way I want them.
How do I get the Cisco to recognize, and use, VLAN1 when I have a trunk defined?