Sup 720 engine question

Unanswered Question
Jul 2nd, 2008

I have two catalyst 6500 switches with sup 720 engines. the sup 720 are used for only l2/3 forwarding. The 6500's are conencted using 10/100/1000 48 ports linecards.

Is there any reason why it is not recommended to connect the 6500's via the sup 720 engines directly?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
Mark Yeates Wed, 07/02/2008 - 09:14

The only reason I see it not being recommended is if there is a supervisor failure, the link connected to the sup would go down. If it is on the 48 port line card a supervisor failure would no have any effect on the link itself in the event of a failure...


Jon Marshall Wed, 07/02/2008 - 15:58


I'm not aware of any recommendation not to connect the switches together with the supervisor ports. If the supervisor fails in your chassis then the 10/100/1000 linecards in that chassis won't work anyway.

In fact there are advantages to connecting via the supervisor ports in that the supervisors will always boot first in the chassis. So as soon as the supervisors are up the switches are aware of each other which can help in STP/routing protocols.

What we did was to interconnect the 2 supervisors with a 1Gb link and then have another 3Gbps connections off a linecard join that etherchannel when the linecards have booted up.


Mark Yeates Wed, 07/02/2008 - 17:40


I really like your idea of using the supervisor ports as part of an etherchannel bundle. I will also agree, as I have not heard that using the supervisor ports are not recommended. Rating as deserved!


rseiler Wed, 07/02/2008 - 20:43

Be very careful using the sup720 uplink ports with most 48-port linecards as the QoS queuing and prioritization of those ports differs significantly. You may need to disable etherchannel consistency checking to get this to work at all anyway.

This is particularly a problem with the 6148 and 6548 GE-TX (10/100/1000) variety of 'junk' blades. Because these modules are only 6-port GigabitEthernet blades (with 6 groups of 8 ports sharing a 1Gb backplane connection), they have significant oversubscription and head-of-line (HOL) blocking issues.

Just an FYI.

francisco_1 Thu, 07/03/2008 - 00:36


My understanding is if i have two sup 720 on each 6500's, only one can be active and the other hot. so only one card can forward at any given time. so if i want to create etherchannel from both sup 720 engines on one chassis againt another two sup 720's on another chassis, i dont see that working because like i said only one sup 720 engine is forwarding on both chassis. right?

also i have limited ports on the sup 720.

1 SPF on it own

1 ethernet and 1 SFP treated as the same port.

2 flash ports

1 console.

so the total uplink i can get is 2gb. I would like to have at least 4GB channel between the sup engines so i dont think that's possble with the sup 720 but possible with the 10/100/1000 lincards. i can have up to 8GB channels. Please advise.

Jon Marshall Thu, 07/03/2008 - 09:28


Firstly didn't realise you had redundant supervisors but principle is same. One will forward other will be in hot standy.

You can create an etherchannel across modules in the same chassis. So you are not limited by the amount of ports on the Supervisor. You have a 1Gb link between your Sup720's. But this is only one link out of 4 that form an etherchannel. When the switch boots the 1Gbps link becomes active first. When the linecard that has the other ports you want in the etherchannel comes on line these ports are then added to the 1Gbps link.

So you are not limited by the number of ports on your supervisor.

Does this make sense ?



This Discussion