lundi, août 23, 2010

Juniper EX-4200 internal PFE routing in stack

During a troubleshooting session on a 10-members Juniper EX-4200 stack, I discovered the use of "show virtual-chassis vc-path source-interface XX destination-interface YY".
This command display the internal path across the EX-4200 PFE chips.
I obtain a result different that the EX-4200 diagram displayed in the O'reilly book "JunOS enterprise Switching" regarding the "Uplink Module".
Here are my results (simplified to a 3-members stack):

The Juniper use an internal routing-protocol for using shortest path between ports (less PFE hop count).
This diagram depends of how you build your stack too: If you use another way for plug your stack-cables, the result will be different.

Here is how to display the path when going from port ge-0/0/0 to ge-2/0/0

user@ex-stack> show virtual-chassis vc-path source-interface ge-0/0/0 destination-interface ge-2/0/0
vc-path from ge-0/0/0 to ge-2/0/0
Hop   Member  PFE-Device  Interface
0       0         1       ge-0/0/0
1       1         4       vcp-1
2       1         5       internal-1/25
3       1         3       internal-2/24
4       2         6       vcp-0
5       2         8       internal-0/24
6       2         7       ge-2/0/0

This means that if only one of the 3 PFE on one of your stack member have a problem, it's all flow that cross this member that will have problem.
You can check internal-PFE communication error with this command:
show virtual-chassis vc-port statistics extensive | match errors

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