6500 X6700, X6800, X6900 line card inter-operation

When deploying line cards and supervisors into a 6500 series chassis there are a number of things to consider. One of which is the line cards you will use and how they will actually operate.

This post specifically talks about the Sup2T because the older SUP720s are pretty much end of life, and if you are still getting hold of them for whatever legacy / governance reasons you probably know all about them anyway so from here on out all references in this post will be assuming we are using a Sup2T.

When deploying a 6500 chassis with a Sup2T you have the choice of the following line cards: X6700, X6800, X6900 and select X6100. There is only one X6700 which isn't compatible, the WS-X6708-10G.

Older DFCs are not compatible, the DFC, DFC2 or DFC3x, this is because DFCs use the same architecture as the PFC on the supervisor and the Sup2T uses a different PFC architecture to older Sups. The Sup2T uses a PFC 4 and as such only DFC4s can operate with it. X6700 cards with DFC3x will have to be upgraded to DFC4s and will function in dCEF720 mode.

X6100 line cards will function in "classic mode"

X6700 line cards which are equipped with CFC will function in CEF720 mode.

X6700/X6800 line cards equipped with DFC4 will function in dCEF720 mode

X6900 line cards which are equipped with DFC4 will function in dCEF2T mode.

X6700 line cards which are upgraded with DFC4 will be functionally equivalent to X6800 line cards but still shown as X6700 as an identity.

CEF720 mode has 1 or 2 x 20Gbps connections to the switch fabric for data forwarding and a connection to the 32Gbps shared bus for control traffic.

dCEF720 mode doesn't connect to the shared bus just the 2 x 20Gbps switch fabric channels. dCEF720 mode has a top throughput of 40Gbps because of the fabric channels, make a note of this when calculating over subscription ratios.

dCEF2T mode supports 2 x 40Gbps channels to the switch fabric

Sup2T switch crossbar fabric:

The Sup2T has 26 fabric channels which each run at 40Gbps, or 20Gbps to provide backwards compatibility with X65700 and X6800 line cards. Each line card slot has 2 dedicated fabric channels so even a 6513 chassis has the full bandwidth available to each port. N.B In a 6513-E chassis slots 7 and 8 are sup only slots because they get only one channel each. The reason for this is because 2 channels are used to connect to the fabric ASIC and Bridge ASIC leaving only 24 channels for slots, but as it is designed in this way the line cards are never affected and always get the full 2 channels each.

This image was taken from the Cisco Sup2T architecture white paper linked below.

The Sup2T architecture White paper is a fantastic resource well worth anyone reading:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/white_paper_c11-676346.html

The other arctiture document worth reading is older and touches on the Sup720, still interesting:

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80673385.html