Layer 2 / Layer 3, routing, default routes, ect..

Question

Ran into an issue this morning at work; We have a firewall, and (2) seperate dell switch stacks. Lets call them stack A and B. From the firewall, I'm trunking vlan 100 to stack A, then trunking it down to stack B. Stack A had an IP address 10.10.100.1. Stack B had an IP address of 10.10.100.3. The firewall has an IP address of 10.10.100.2. This weekend, I removed stacks A IP address and moved it to stack B, so now stack B was 10.10.100.1, A had no IP, and the firewall was still .2. Heres where we ran into issues; on stack A we have a bunch of other vlans... 101,102,103,ect ect.. none of them we're able to get to the internet. Anything on the 100 VLAN was able to. It is my understanding that even though stack A did not have an IP address, traffic should of been able to flow freely throughout the network because I was trunking VLAN 100 from the firewall to stack A, and then downto stack B. FW <--> Stack A <--> Stack B When someone on VLAN 102 wanted to get to google; its default gateway was on stack A, IE 10.10.102.1; and on stack A there is a default route of; ip route 0.0.0.0 0.0.0.0 10.10.100.2 && name 'Datacenter VLAN'routingip ripexit But it was not working; so I gave the 100 VLAN an IP address and then it started working. I dont know why. Thanks for any help!

jerhoman · Answer

Is it because once traffic from a VLAN other than 100 hit the first floor stack, the default gateway pointed to an address on the 100 VLAN and it did not know how to get there?

Should I of pointed the 1st floor stack default gateway down to 10.10.100.1 ? Stack B, or 10.10.100.1, has a default route that points to the firewall as well.

Was it because I did not have a L3 IP address on stack A for VLAN 100 that made the default route null?

jerhoman · Answer

This was indeed why, I did not have a IP associated with vlan 100 on stack a.

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