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New Member

Why have sub ints on a fa?

I understand the sub-ints on  aserial WAN link, usually for frame-relay, but why the sub-ints on the fa? And how is it implemented on the LAN?  With a FR switch?

R#sh ip int br

Interface                  IP-Address      OK? Method Status                Protocol

FastEthernet0/0            unassigned      YES manual up                    up

FastEthernet0/0.1          10.111.80.1     YES manual up                    up

FastEthernet0/0.20         10.114.1.113    YES manual up                    up

FastEthernet0/1            unassigned      YES NVRAM  administratively down down

Serial0/0/0                unassigned      YES NVRAM  up                    up

Serial0/0/0.20             152.162.251.138 YES NVRAM  up                    up

Loopback0                  10.255.111.82   YES NVRAM  up                    up

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Why have sub ints on a fa?

Hello Ron,

Subinterfaces on FastEthernet interfaces are used for VLANs. If you want your router to be a member of multiple VLANs and provide inter-VLAN routing, you need to create these subinterfaces, one for each VLAN the router should be a member of. The IP address of a particular subinterface can then be used by stations in the associated VLAN as their default gateway.

Best regards,

Peter

3 REPLIES
Cisco Employee

Why have sub ints on a fa?

Hello Ron,

Subinterfaces on FastEthernet interfaces are used for VLANs. If you want your router to be a member of multiple VLANs and provide inter-VLAN routing, you need to create these subinterfaces, one for each VLAN the router should be a member of. The IP address of a particular subinterface can then be used by stations in the associated VLAN as their default gateway.

Best regards,

Peter

New Member

Why have sub ints on a fa?

OH!!!

ROAS. It skipped my mind. Thanks Peter.

Cisco Employee

Why have sub ints on a fa?

Hi Ron,

You are very much welcome. Thank you for the rating!

Best regards,

Peter

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