No CAM Entry for remote end IP on L3 P-2-P link

Answered Question
Dec 7th, 2009
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I have just noticed that there is no entry in the cam table for P-2-P ethernet links. I see an arp entry however there is no cam entry for the remote end's ip in the cam table. Everything is working normally and am just wondering if this has something to do with the fact that it is point-to-point. What is the actual reason for this behaviour? In this particular instance the devices on either side are 6500 switches and the link itself is a Gig-E link however i also notice the same behaviour on other devices where the link is L3 P-2-P. Thx for your help.

Correct Answer by Giuseppe Larosa about 7 years 5 months ago

Hello Vdadlaney,


a CAM table entry should exist for each L2 port belonging to a L2 broadcast domain (a L2 vlan object).


No CAM table entries exist for L3 point-to-point links because they are out of the vlan space think of them as using a special reserved vlan value to declare this.


About L2 point-to-point links: CAM tables entries are organized based on vlan-ids.

If a multilayer switch has only one L2 port in vlan x it is not performing bridging for that vlan.

A possible explanation can be that CAM entries are triggered by the existance of at least two L2 ports belonging to vlan x, so that the question of out what ports to propagate received frames start to be meaningful.

With only one port there is no need to create cam entries there is no other port where to propagate frames.


Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Mon, 12/07/2009 - 10:02
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Hello Vdadlaney,


a CAM table entry should exist for each L2 port belonging to a L2 broadcast domain (a L2 vlan object).


No CAM table entries exist for L3 point-to-point links because they are out of the vlan space think of them as using a special reserved vlan value to declare this.


About L2 point-to-point links: CAM tables entries are organized based on vlan-ids.

If a multilayer switch has only one L2 port in vlan x it is not performing bridging for that vlan.

A possible explanation can be that CAM entries are triggered by the existance of at least two L2 ports belonging to vlan x, so that the question of out what ports to propagate received frames start to be meaningful.

With only one port there is no need to create cam entries there is no other port where to propagate frames.


Hope to help

Giuseppe

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