[j-nsp] juniper cisco switch interconnection

[Ben Dale]

ooh VSTP/PVST+ interop.  Boy have we had some fun here over the years..

Cisco PVST+ sends IEEE and Cisco BPDUs on the *native* VLAN and Cisco BPDUs for each VLAN that is tagged on an interface.
 
Juniper VSTP only sends  IEEE BPDUs on the native VLAN 1 (or did as of 11.4) but sends Cisco BPDUs for each tagged VLAN.

A gotcha to watch out for is if you are using "default" VLAN in Junos as your native, you need to manually set the VLAN-ID to 1 or the VSTP config will not pick it up:

set vlan default vlan-id 1

There is a change in 12.2 regarding something similar to this:

"VSTP compatibility with Cisco PVST+—When you configure VSTP using the set protocol vstp vlan all configuration mode command, VLAN ID 1 is now excluded, thus making Junos OS VSTP compatible with Cisco PVST+. To include VLAN ID 1 in the VSTP VLAN, you must now add it explicitly using the set protocol vstp vlan 1 configuration mode command."

If you're in a pure Juniper environment, you don't need to worry too much though - as long as you have a common native VLAN (or even if you have none) everything generally works pretty well provided you make sure you're not running an EX software version affected by this bad boy:

http://kb.juniper.net/InfoCenter/index?page=content&id=KB22111&cat=EX_SERIES&actp=LIST&smlogin=true

If your VLAN count is getting up over 100, consider MSTP - the CPU thrashing on a 3550 or 3750 when they all reconverge has some NASTY side-effects (like delaying the sending of BPDUs, causing the issue to spiral even further).


On 11/12/2012, at 7:28 AM, Mike Azevedo <mikea615 at iristransport.com> wrote:

> you can bcast storm your network to a halt if you are not careful. Use VSTP on juniper side to match the cisco PVST+. I believe Juniper's RSTP uses one instance of spanning tree over the physical network not an instance per vlan like cisco's implementation. I would also watch out for vlan 1. 
> 
> 
> 
> ----- Original Message -----
> 
> From: "Benny Amorsen" <benny+usenet at amorsen.dk> 
> To: "harbor235" <harbor235 at gmail.com> 
> Cc: "Juniper List" <juniper-nsp at puck.nether.net> 
> Sent: Monday, December 10, 2012 3:16:10 PM 
> Subject: Re: [j-nsp] juniper cisco switch interconnection 
> 
> harbor235 <harbor235 at gmail.com> writes: 
> 
>> Has anyone connected a Juniper EX series switch with a Cisco switch (I have 
>> a 3550)? 
> 
> Yes 
> 
>> Do you use a standard crossover cable? MDIX? 
> 
> I have only attempted 1Gbps, that just worked with a straight cable. 
> 
>> Any Layer 2 issues with RSTP and PVST+? 
> 
> It seems to work so far... 
> 
>> Any specific configuration required to make it work? 
> 
> Avoid VLAN 1. You can probably make VLAN 1 work if you try, but for me 
> it was easier to simply not use it. 
> 
> 
> /Benny 
> 
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