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Routing between 3 subnets - third network not being routed

Posted on 2010-03-24
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Last Modified: 2012-06-27
I have 3 subnets that I'm trying to route between using 2 Cisco 2811 routers, each with a 4-port WIC card.
Subnet 1 (172.16.0.0/21) is physically attacted to router C on fe0/0.
Subnet 2 (172.16.8.0/21) is physically attached to router B on fe0/0.
Subnet 3 (172.16.16.0/21) is physically attached to router B on fe0/0/0 via VLAN1 on the WIC card.
Subnet X (192.168.50.0/30) is a stub network to connect the two routers using fe0/1.

My problem is this:
Subnets 1, 2 and X can see each other just fine.
Subnet 3 is invisible to all the other subnets-- it cannot see any other subnet and cannot be seen from any other subnet. Yet, the interface address of subnet 3 *is* visible. A trace to the interface shows this:

Tracing route to 172.16.16.1 over a maximum of 30 hops
  1    <1 ms    <1 ms    <1 ms  172.16.0.7
  2     1 ms     1 ms     1 ms  172.16.16.1

A trace to an address within subnet 3 shows this:

Tracing route to 172.16.16.72 over a maximum of 30 hops
  1    <1 ms    <1 ms    <1 ms  172.16.0.7
  2     2 ms     1 ms     1 ms  192.168.50.1
  3     *        *        *     Request timed out.

I've pored over the configuration of all routers and cannot find a problem. I would really appreciate some help. Config files for both routers are attached with sensitive info removed.
config.zip
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Question by:Brian Longworth
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Expert Comment

by:Rick_O_Shay
ID: 28474697
On the VLAN 1 interface shouldn't there be a no shutdown?
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Author Comment

by:Brian Longworth
ID: 28474828
No. Doesn't make a difference. "No" just removes the shutdown command.
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Expert Comment

by:Rick_O_Shay
ID: 28475404
Doesn't removing the shutdown enable IP on the VLAN interface?
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Author Comment

by:Brian Longworth
ID: 28476001
Just for fun, I tried it. No change in either the config or in functionality.
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Expert Comment

by:Rick_O_Shay
ID: 28477213
Is there a device connected to VLAN1 to bring it active?
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Author Comment

by:Brian Longworth
ID: 28477798
Yes. Connected into the switch for the subnet.

sh int fastethernet0/0/0
FastEthernet0/0/0 is up, line protocol is up
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Brian Longworth earned 0 total points
ID: 28486940
I fixed it myself. A tech had configured the port for subnet 3 incorectly and missed the VLAN tagging.
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