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Encapsulation Dot1q for a trunk

marvin1234
Level 1
Level 1

We have a 6500 Dist Switch that connects to two access switches. We're trying to Multicast image the machine on the access switches and we notice that there is  an issue where machines on Switch A can be imaged using multicast But machines on switch B cannot be imaged. The only difference that I have found in the configs are on the trunk links/

The 6500 has to Switch A

switport mode trunk

switchport trunk encap dot1q

The 6500 has to Switch B

switport mode trunk

switch A

switport mode trunk

switchport trunk encap dot1q

Switch B

switport mode trunk

switchport trunk encap dot1q

The only command missing on trunk config on 6500 dist Switch to switch B is switchport trunk encap dot1q . Could this cause Multicast issues>? Everything else is working fine. No issues.

3 Replies 3

Leo Laohoo
Hall of Fame
Hall of Fame
The only command missing on trunk config on 6500 dist Switch to switch B is switchport trunk encap dot1q . Could this cause Multicast issues>

Maybe the 6500 line card only support 802.1q trunking.  To verify, enter the command "sh interface trunk".

Yep, you're right Leo. Any ideas as to why Multicast would work to one switch and not the other? All the config is identical

Is IGMP enabled on switch B?

Are the sender and receiver both in the same vlan?

Is the 6500 doing layer-3 (SVI)?

HTH

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