VLAN tagging on 9216 byte jumbo frames

[robmurphy]

I am looking into interworking some new transmission equipment over gigabit ethernet with jumbo frames.

From a quick search it seems that 9216 byte is accepted as the 9k jumbo frame size.

What I would like to know is what happens with the Cisco catalyst 6500 series switches if you decide you want to add a VLAN tag to the outgoing frame.

Also what would happen if a tagged 9k packet arrived at the Cisco, as the frame would be 9216 + 4 = 9220.

Are there any differences on the Cisco kit between Copper and optical interfaces for Gigabit ethernet?

Thanks in advance for any help

Rob

 

[nightowl]

The 9216 bytes is for the IP packet only. On top of the 9216 bytes you still add 14 bytes for the Ethernet header, 4 bytes for CRC, and trunking header. So in your case, the Ethernet frame size is 9238 bytes. As for the media type, it does not matter. The real dependency will be the phy on the line card. So, you will need to check the documentation for your line card to see what is supported.

 

[robmurphy]

OK a little further digging shows that the Catalyst 6500 max frame size is 9216 + 18 bytes for the ethernet header and CRC trailer.

The same questions still arise.

What happens if you try to send/receive with the IEEE 4 byte VLAN tag when the frame is already 9216 bytes?

Is the 9216 a hard limit meaning if you want to tag the frames you must limit the frame size to 9212 to allow for the 4 byte VLAN tag?

Rob.

 

[nightowl]

Like I said before, the 9216 bytes is for the IP packet only. You can successfully transmit 9238 byte frames on a supported line card on a 6k. That is including 9216 bytes for the IP packet, 14 bytes for the Ethernet header, 4 bytes for CRC and 4 bytes for the dot1q header. Hope that helps!