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Tagged traffic through CM and CMTS !

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astrit
Tagged traffic through CM and CMTS !

Hi list,

I have a CPE (Cisco Router 1841) behind a CM which has an interface with 802.1Q encapsulation, and it is in VLAN 27.
Another Cisco 1841 is connected in the same switch where CMTS is connected, and also has an interface with 802.1Q encapsulation, and VLAN 27. The Switch ports where CMTS and the Cisco 1841 are connected are configured in trunk mode and they allow VLAN 27 to pass. The schema should look like below:

But the routers doesn't ping each other. When I remove 802.1Q encapsulation the Routers can see each other. It looks that CMTS or Cable Modem is dropping packets when they are encapsulated with 802.1Q.
Could anybody help me please?

Regards,
Astrit

Anonymous (not verified)
Tagged traffic through CM and CMTS !

First of all you should notice model of your CMTS.
Not all CMTS is VLAN capable.

Try a simple thing - instead of Cisco 1841 behind CM install any PC with unix/linux and tcpdump tool and listent traffic via
tcpdump -i eth0 -n
try to determine - doest the traffic on network interface vlan tagged or untagged.
on windows you can use network monitor or windump32 (tcpdump for windows)

I think the reason is that your CMTS is unable to work with VLAN.