uP with two ethernet ports (MACs)

You haven't said anything about size or application. The AVR32 AP processors have two network ports, but you'll need external memory.

An alternative to using two MACs could be to use a microcontroller with a single MAC and a managed switch chip set up with different VLANs on each port.

Broadcom has some (IIRC they're pretty expensive -- $40+).

Motorola also has a new family of Coldfire parts with two MACs.

Freescale also has PowerPCs with dual MACs

ARM

ng.

Interesting :-) I understand that a managed switch with VLANs allows you to run these different LANs on the same hardware, making the individual VLAN assignments configurable.

Can you pls provide with a link or document that talks in detail about this alternate mechanism of using single MAC ?

Thx in advans, Karthik Balaguru

You should have no problems finding information about 802.1Q VLANs on google or wikipedia, and there is lots of information about it for using VLANs with Linux (I've used them on several Linux setups). However, I haven't used them with small micros at all, and I don't know what sort of support there is in existing RTOS's and networking stacks, or how much work it would take. I only know that it is a possible solution - the OP will have to do some research here.