3500yl J9310A Connection Issue

[BrianPC]

Greetings all,

I am experiencing a wierdness I am hoping this forum can assist me with:

2 offices, A and B, linked by a Comcast "ENS" private link. Both offices have 3500YL J9310A switches terminating the ends of the private link. I am assured by Comcast this is an ethernet link and I should treat it as a LAN, and both switches see thier ports as up. IP routing is enabled on both switches.

The config for the port is this:

Office A: - Note there are 2 ports in this as in troubleshooting I 'tried a different port':

vlan 10
name "Inter-Office-Link"
untagged 7-8
ip address 172.31.1.1 255.255.255.248

Office B:

vlan 11
name "VLAN11"
untagged 37
ip address 172.31.1.2 255.255.255.248

Note: I have used the "VLAN 10" on both sides in my troubleshooting too. Same results.

The issue is this: 

Only one side will put the route into the routing table. If I disable the port in office B, the switch in office A looks like this:

sh ip route

IP Route Entries

Destination Gateway VLAN Type Sub-Type Metric Dist.
------------------ --------------- ---- --------- ---------- ---------- -----
0.0.0.0/0 192.168.1.2 1 static 1 1
10.250.0.0/24 192.168.7.254 200 static 1 1
127.0.0.0/8 reject static 0 0
127.0.0.1/32 lo0 connected 1 0
172.31.1.0/29 Inter-Office... 10 connected 1 0
192.168.0.0/22 Data 1 connected 1 0
192.168.5.0/24 Floor5 5 connected 1 0
192.168.7.0/24 PhoneVLAN 200 connected 1 0
192.168.21.0/24 192.168.1.2 1 static 1 1
192.168.27.0/24 192.168.1.2 1 static 1 1
192.168.31.0/24 192.168.1.2 1 static 1 1

If I enable the port on side B then side B will put the route in and side A will take the route out, i.e. the most recently enabled port's host switch will have the route and the other side won't. I can't get both sides to hold the route when both ports are up. Right now the VLAN settings are dissimmilar but I've tried them exactly the same (except for IP address of course).

Thanks in advance for any assistance you can provide!

Regards,

BPC

[BrianPC]

I solved it. When in doubt, check spanning-tree. Once I put in:

spanning-tree <port#> bpdu-filter

on both sides it is all up.

It has been a while since I have been a netwok guy...rust falling off in HUGE flakes!!

Regards,

BPC

[parnassus]

Hi! glad you fixed.

Technically speaking if your switches are interconnected via a Layer 2 link and if both manage the same VLANs is not necessary to enable the IP Routing feature on both...just on the one that need to be the Core (routing for its VLANs' SVI, (R)STP with priority 0 to be the root of the Spanning Tree)...so the uplink will become (as it is de-facto today) just a Layer 2 extension between both peers...so why IP routing on the second switch? You just need to permit (tag) required VLANs on the uplink to have them extended on the second switch at remote end.

I don't see you used to connect both by Layer 3 Routing...since the IP address 172.31.1.1/255.255.255.248 was assigned to VLAN 10 on Switch 1 and the 172.31.1.2/255.255.255.248 was assigned to VLAN 10 on Switch 2 BUT there is (are) static routes between both using those IP addresses as next hop.

This means that you simply have VLAN 10 on both, both VLAN 10 have SVI within the same subnet (172.31.1.0/29 <- it's typical of a Transit VLAN but here it looks like you're exactly using a Transit VLAN by routing it), the uplink is untagged on VLAN 10 (so only that VLAN is permitted) but no crossing static routes exist (on Switch 1: Switch 1 to Switch 2 and vice-versa on Switch 2: Switch 2 to Switch 1).