Any restrictions on SubIf Inter-VLAN Routing?

[dannydanny]

Hi All

I was looking at purchasing a 2811 router with additional Ethernet ports for routing between LANs. The only cards available for the 2800 series seems to be HWIC 'switch' cards. I understand that these cards also provide routing functionality thru. a Vlan interface, but can not see the point in purchasing this card if I already have ports available on an existing Cat switch and bit rate is not an issue. However, this still leaves me short of ethernet interfaces, so my question is: does routing between vlans on the subinterfaces of a trunk offer all the functionality (e.g. HSRP, NAT etc, etc), available from routing between separate L3 ethernet interfaces ? Can I configure the sub-interfaces with the full range of features available to L3 interfaces - (NB: accepting the that there is an aggregate bit rate for the trunk port).

Thanks in Advance

[ankurbhasin · Accepted solution]

Hi Danny,

Not the full range of features are supported. Some are supported but with some limitations.

1) Like for HSRP

HSRP groups on subinterfaces must have a group number unique among all other groups on all subinterfaces on the same main interface. This is because subinterfaces do not receive a unique SNMP interface index. If you had two groups with the number N on different subinterfaces, then in the MIB, group N on sub-interface 1 and group N on sub-interface 2 would appear to be the same group.

Check this link

http://www.cisco.com/warp/public/619/hsrpguidetoc.html#subinterfaces

2) For QOS : CBWFQ : Not supported on subinterfaces

Check this link

http://66.102.7.104/search?q=cache:rgSfUhmPNlQJ:www.show.it/ftp/documenti/Cisco/QoS/qos_subint.pdf+features+supported+on+sub+interfaces+of+router&hl=en#3

3) Talking about NAT...yes you can apply NAT on subinterfaces

Check this link out

http://www.cisco.com/warp/public/556/nat-faq.html#Q8

HTH

Ankur