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New Member

How to create sub interfaces


Can someone tell me how to create sub interfaces in a 2500 series router, wihch doesn't have fast ethernet. Well, it's like this. I can create sub interfaces, but the moment I try giving an IP address, it says, that I have to enable, 802.10, ISL or 802.1Q

Please give me a solution for this.

I also can give more than one secondary IP addresses on Ethernet interface. i.e. One primary address, and at least two secondary addresses. Is that possible or is it some sort of a bug in the IOS image?



Re: How to create sub interfaces

Sub-interfaces are only used in Ethernet for VLAN / trunking (ISL or 802.1q "Dot1q").

To add additional addresses to an interface add the keyword "secondary" at the end of the line. You can have multiple additional addresses, but you still use the "secondary" keyword.

i.e., ip addr (this is primary address)

ip addr secondary (second address)

ip addr secondary (third address)

Since you are only adding addresses to a single physical or logical interface, the encapsulation and other parameters must all be the same.

Good Luck


New Member

Re: How to create sub interfaces

Hi Scott

Thanks a lot for your info. But I have a doubt here. In a 2600 series router I think I could creat sub-interfaces and give an IP address to that sub-interface although I cannot do it in this 2500 series. Is it may be because 2600 series has fast ethernet?

We can create sub-interfaces even in the serial interfaces can't we, when we configure Frame-Relay?

Thanks a lot for your previous answer.


New Member

Re: How to create sub interfaces

Hello Omal,

If I remember from a long time, the subinterface on a Cisco 2500 Ethernet interface is only to run different encapsulation of the IPX protocol. I do not beleive you can create subinterface for IP. The cisco 2500 does not support ISL or Dot1Q encapsulation on the Ethernet interface.



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