[j-nsp] EX_4500 Dot1q-LAG and MSTP Query !

[Chuck Anderson]

On Fri, Jan 27, 2012 at 12:25:18PM +0530, vaibhava varma wrote:
> In the Juniper EX-4500 series switch if we are using a LAG say ae1 and
> want to run dot1q peering on it with MX-240 upstreams is it necessary
> to create the L2 VLAN also in the Switch e.g
> 
> set interfaces ae1 vlan-tagging
> set interfaces ae1 description Interconnection-to-bbsw01-ae1
> set interfaces ae1.3042 vlan-id 3042
> set interfaces ae1.3042 description Interconnect_Control_bbsw01
> set interfaces ae1.3042 family inet address 172.16.0.34/30
> 
> Does the VLAN 3042 needs to be added separately in the VLAN Database.
> My understanding was that is not needed .

Incorrect, you need to define it in the switch simply like this:

set vlans FOO vlan-id 3042

> ALso regarding the MSTP configuration is it mandatory to create all
> the L2 VLANs in the VLAN Database for which we creating
> instance-to-vlan mapping.

No.  You DO have to specify the entire list of VLAN IDs you want to
associate with each MSTI (this is a requirement of any MSTP switch),
but you do NOT need to create those VLANs under "edit vlans" unless
you are going to use them to forward traffic on some interfaces on
that switch.

> In a bigger network with lots of switches why do we need to create
> those L2 VLANS on a Switch for which its not catering any traffic.

You don't.  You just have to map them to each MSTI so that the MSTP
Configuration Digest is calculated identically on all switches in the
entire MSTP Region.  If you don't have a matching digest
(i.e. matching VLAN <--> MSTI associations for every MSTI) then each
switch with a different digest will create a boundary and split the
network into multiple separate MSTP Regions.  You can't load-balance
VLANs between multiple links across such a boundary.