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New Member

Problems with ISL/Dot1Q Trunking

Hi there,

I have the following setup:

7505==3550a==3550b======>cat5 to transit network

^ ^ ^

1Q ISL 1Q

VLANs 708 and 709 are configured on the 7505 as dot1q subinterfaces.

When the cable is connected to 3550b cat switch I am not able to ping our transit provider network (well I lie, I get the first 5 pings through and that is all!!!).

When the cable is connected to 3550a cat switch it all works fine.

Is ISL between 3550a and 3550b causing the problems or is it something else? Oh, the trunking between these two switches are also configured as single EtherChannel link.

Thanks,

Chee.

2 REPLIES

Re: Problems with ISL/Dot1Q Trunking

Hi,

the ISL itself should be no problem. (You can check it if you change the trunking between 3550s to dot1q. But I don't think it would fix the problem.)

I'd try to check the etherchannel first.

Are both sides configured identically?

What port type are you channelling? (I remember some limits, GigaStack GBICs not allowed to etherchannel, e.g.).

What happens when you interconnect 3550s via only one physical line?

Regards,

Milan

New Member

Re: Problems with ISL/Dot1Q Trunking

Thanks for your reponse!!! I am using the GBIC SX port, however this setup is in our production evironment and traffic flows across the switches OK.

I will try to reproduce this fault using none production switches, so I can isolate it.

Thanks,

Chee.

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