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Stupid Question about a 3750 Stack..

Michichael
Level 1
Level 1

Alrighty then. I've been passed the ball on this new network infrastructure the company is doing. And I can't, for the life of me, figure out exactly what's wrong here.

Situation: Switch Stack configured to 10.20.13.2.

MPLS Router is 10.20.13.1

VoIP VLAN Configured for 10.90.0.1/24

And we're adding a wireless DSL router as an alternate gateway/internet source for specific access only (IT prefers not to use the MPLS thanks to better bandwidth from DSL...)

I've got it configured on VLAN 91, with 10.91.0.1 being the switch, 10.91.0.254 being the router. The reason for this is we want it to be separate from the rest of the networks, no unsolicited traffic coming in, etc. It seems to work great! I can ping from the 10.20.13.x subnet to the router. It responds. Every thing's happy... until I try using it as a default Gateway.

Here's the problem: I configure a computer with 10.91.0.254 as the default gateway, but when I try to tracert out, it goes through the MPLS! Here's the info...

IP Address: 10.20.13.203

Subnet Mask: 255.255.255.0

Default Gateway : 10.91.0.254

-------------------------------

Tracing route to vnsc-bak.sys.gtei.net [4.2.2.2]

over a maximum of 30 hops:

1 <1 ms <1 ms <1 ms 10.20.13.1

2 4 ms 4 ms 4 ms 74.8.108.21

And what's weird is if I configure it as a gateway, and try to ping it, it gives me 10.20.13.1: Destination net unreachable. But if it's not set as the gateway, I can ping it just fine. Any ideas?

I will note: by default the gateway is the switch: 10.20.13.2, and when that is the gateway I can ping 10.91.0.254. I attempt to set the gateway as 10.91.0.254 and it stops talking to the switch and tries going straight through the MPLS.

When the default gateway is 10.20.13.2, it goes from that to the internet. When it is 10.91.0.254 it tries going through 10.20.13.1, our MPLS connection to the internet. Shouldn't it, if it is 10.20.13.2, be going from 10.20.13.2 to 10.20.13.1 to the internet? I'm confused!!!

What am I missing?

16 Replies 16

Yes, I configured the static route back. Sec...:

Route List

Subnet IP Subnet Mask Gateway Interface

127.0.0.1 255.255.255.255 127.0.0.1 lo0

10.91.0.254 255.255.255.255 10.91.0.254 bridge0

10.20.13.0 255.255.255.0 10.91.0.1 --

The last is the one I added. Naturally I removed the public IP parts.

Wow. What you're describing sounds sort of like proxy-arp, 'cept the host's mask is too long. I think we're missing something in the description here cause it...well it doesn't make sense. To clear it up I think diagrams and configs will be necessary.

Best thing do to is to set the thing to best practices, hosts' gateway on same subnet with hosts etc. Then you ip-policy the hosts you want using the DSL to the DSL router.

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