Inter-Vlan Routing

[v.dadlaney]

Hi, I have a 2912XL-EN switch. I am trying to get a router that supports fast ethernet to do inter vlan routing and I was wondering if the 1720-21 would be a good low-cost solution. Also, does the 1720-21 support ISL encapsulation or only 802.1q. Would the 2620 be a better alternative? I am doing this for home lab I have setup and well the 1700 would seem to be the cheaper solution. I don't think the 2500 come with fast ethernet interface. Atleast not the ones that I have and it is my understanding that in order to do trunking you need to have a fast ethernet link. Appreciate the help. Thanks

[mark-obrien]

Hello,

I just tried configuring ISL on a sub-interface in a 1720 and struck out. This is with IOS version 12.1, so it is a new enough IOS. The router rejected any encapsulation command on the sub-interface. Unless anyone else knows better, it looks like you may need the 2620.

Good luck.

Mark

[Prashanth Krishnappa]

1700 series does not support trunking

[gaban]

I have done this before on a 1710 with 2 vlans on a sub-interface I think I did dot1q.

[Prashanth Krishnappa]

Not supported.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/relnote/1700ser/c1720/rn1700t.htm#xtocid62

Are you sure it was a 17xx?

[ggersch]

1700 class routers only do 802.1q trunking. You will need a 2600 class or better for ISL trunking. There might be IOS feature sets necessary as well. In all cases, you can only do trunking on Fast Ethernet interfaces.

Part of what determines ISL support is whether the ethernet chipset can handle the altered length ISL frames.

Greg

[Prashanth Krishnappa]

Where did you find this info. 1720/1750 does *NOT* support trunking. The release notes should clarify things

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/relnote/1700ser/c1720/rn1700t.htm#xtocid62

It is a hardware limitation and no software upgrade will give you trunking capabilities on this platform