cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
1227
Views
0
Helpful
4
Replies

2851 looping with bvi interface

gregsmales
Level 1
Level 1

Hi all,

Just wondering if someone can provide some assistance with my issue.

Just installed a new 2851. Both ethernet interfaces (gi0/0 & gi0/1) are configured for a bridge-group. Both of these ports are connected to a 3750 switch.

The issue is when I connect both physical cables to the gi0/0 and gi0/1 it creates a loop. Disconnect one of them and it's fine. It appears as though spanning-tree is not working properly.

Can anyone suggest a place for me to look at within my config? (Router or switch). Some of the config below:

2851 router:

interface GigabitEthernet0/0

no ip address

duplex auto

speed auto

no mop enabled

bridge-group 140

interface GigabitEthernet0/1

no ip address

duplex auto

speed auto

no mop enabled

bridge-group 140

interface BVI140

description VLAN 140

ip address 10.1.1.70 255.255.248.0

no ip proxy-arp

ip nat inside

ip ips sdm_ips_rule out

ip virtual-reassembly

zone-member security in-zone

ip route-cache flow

3750:

interface GigabitEthernet2/0/31

description Cisco 2851 Router

switchport access vlan 140

switchport mode access

switchport block multicast

switchport block unicast

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

queue-set 2

mls qos trust cos

auto qos voip trust

storm-control broadcast level 1.00

spanning-tree guard root

interface GigabitEthernet2/0/32

description Cisco 2851 Router

switchport access vlan 140

switchport mode access

switchport block multicast

switchport block unicast

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

queue-set 2

mls qos trust cos

auto qos voip trust

storm-control broadcast level 1.00

spanning-tree guard root

Thanks

1 Accepted Solution

Accepted Solutions

The router isn't running any spanning-tree therefore the switch is not able to block one port to prevent the loop.

Can you post the router's entire config ?

You must have

bridge 140 protocol ieee

bridge irb

bridge route ip

on the router's config.

View solution in original post

4 Replies 4

Edison Ortiz
Hall of Fame
Hall of Fame

Can we see the show spanning-tree output from both devices ?

output from 2851: (however only one interface out of the two is currently active)

2851-01#sh spanning-tree

No spanning tree instances are running.

output from 3750: (the 2851 is connected to gi2/0/31 and gi2/0/32)

VLAN0140

Spanning tree enabled protocol rstp

Root ID Priority 140

Address 0013.c386.ab40

Cost 3

Port 616 (Port-channel1)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32908 (priority 32768 sys-id-ext 140)

Address 0014.a9ec.fd00

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

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

Gi1/0/16 Desg FWD 19 128.16 Edge P2p

Gi1/0/17 Desg FWD 19 128.17 Edge P2p

Gi1/0/18 Desg FWD 19 128.18 Edge P2p

Gi1/0/19 Desg FWD 100 128.19 Edge Shr

Gi1/0/21 Desg FWD 19 128.21 Edge P2p

Gi1/0/40 Desg FWD 19 128.40 P2p

Gi1/0/42 Desg FWD 19 128.42 P2p

Gi1/0/44 Desg FWD 19 128.44 P2p

Po1 Root FWD 3 128.616 P2p

Po2 Desg FWD 3 128.624 P2p

Po3 Desg FWD 3 128.632 P2p

Gi2/0/9 Desg FWD 4 128.61 Edge P2p

Gi2/0/10 Desg FWD 19 128.62 Edge P2p

Gi2/0/11 Desg FWD 19 128.63 Edge P2p

Gi2/0/12 Desg FWD 4 128.64 Edge P2p

Gi2/0/13 Desg FWD 4 128.65 Edge P2p

Gi2/0/14 Desg FWD 4 128.66 Edge P2p

Gi2/0/17 Desg FWD 4 128.69 Edge P2p

Gi2/0/18 Desg FWD 19 128.70 Edge P2p

Gi2/0/19 Desg FWD 4 128.71 Edge P2p

Gi2/0/22 Desg FWD 4 128.74 Edge P2p

Gi2/0/31 Desg FWD 4 128.83 P2p

Gi2/0/39 Desg FWD 4 128.91 Edge P2p

Gi2/0/40 Desg FWD 19 128.92 P2p

Gi2/0/41 Desg FWD 4 128.93 Edge P2p

Gi2/0/42 Desg FWD 19 128.94 P2p

Gi2/0/44 Desg FWD 19 128.96 P2p

The router isn't running any spanning-tree therefore the switch is not able to block one port to prevent the loop.

Can you post the router's entire config ?

You must have

bridge 140 protocol ieee

bridge irb

bridge route ip

on the router's config.

Ok, I had:

bridge irb

and

bridge 140 route ip

However I didn't have:

bridge 140 protocol ieee

I added the above into the config, and spanning-tree kicked in. Then connected the second physical link to the router and spanning-tree blocked the second port. All working perfectly now.

Thanks a lot for your help!

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: