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late dhcp responses

I installed a 2Gb/s etherchannel link between 6509 and Nortel Passport 8610. Nortel works for L3 switching and 6509 only for L2 as a distribution layer backbone. Also 6509 use 2 MST instances. There is a dhcp-server behind a firewall which is connected to nortel through GigE.

When I try to obtain IP address from dhcp server on my pc, sometimes it gets timeout. Sometimes tooks about 30 second. There is no traffic over the link between nortel and 6509 and a client which is connected to nortel backbone obtains IP address in 5 seconds from te same server. What could be the problem? I am messed with forcing 6500 work as a L2 switch. Is this possible? What must I do to force 6500 for working as L2 switch even if it is configured with SUP720 and MSFC3?

This is a temporary solution for or customer who runs Nortel and plan to migrate Cisco. Therefore any help would be muchly appreciated.

rgds

1 ACCEPTED SOLUTION

Accepted Solutions
VIP Purple

Re: late dhcp responses

Hello,

can you check if the client ports on the Cisco configured with 'spanning-tree portfast' ?

Regards,

GP

2 REPLIES
VIP Purple

Re: late dhcp responses

Hello,

can you check if the client ports on the Cisco configured with 'spanning-tree portfast' ?

Regards,

GP

Re: late dhcp responses

Sounds like a known problem. On a non-configured switchport spanning tree enforces a 30s delay in forwarding when the link comes up (i.e. when you switch on the PC). This causes dhcp timeouts in about 80% of all cases.

However, there is a work-around ;-)

Please check that you have "spanning-tree portfast" active on all dhcp-requesting clientports.

Regards,

Leo

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