Dear Giuseppe,

I have configured the routers and the bridge mode configuration is working fine. I can ping both routers.

But there is a problem occurring.

When I connect the second router (Router B)to its LAN, there is no more connection. I cannot reach it anymore. There seems to be a STP loop.

Find below the configuration of both routers:

RouterA#

bridge irb

!

!

!

interface GigabitEthernet0/0

description 'Connection To LAN'

no ip address

duplex auto

speed auto

bridge-group 1

!

interface GigabitEthernet0/1

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/0/0

no ip address

shutdown

clock rate 2000000

!

interface GigabitEthernet0/1/0

description 'Fiber Optics Link'

no ip address

negotiation auto

bridge-group 1

!

interface BRI0/2/0

no ip address

encapsulation hdlc

shutdown

!

interface BVI1

ip address 172.18.12.12 255.255.252.0

arp timeout 300

!

ip forward-protocol nd

!

!

ip http server

ip http authentication local

ip http timeout-policy idle 60 life 86400 requests 10000

!

!

!

control-plane

!

bridge 1 protocol ieee

bridge 1 route ip

Router A#sh spanning-tree summary

Root bridge for: Bridge group 1.

PortFast BPDU Guard is disabled

UplinkFast is disabled

BackboneFast is disabled

Name Blocking Listening Learning Forwarding STP Active

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

Bridge group 1 0 0 0 2 2

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

1 Bridge Group 0 0 0 2 2

RouterB#

bridge irb

!

!

!

interface GigabitEthernet0/0

description 'Connection To LAN'

no ip address

duplex auto

speed auto

bridge-group 1

!

interface GigabitEthernet0/1

no ip address

shutdown

duplex auto

speed auto

!

interface Serial0/0/0

no ip address

shutdown

clock rate 2000000

!

interface GigabitEthernet0/1/0

description 'Fiber Optics Connection'

no ip address

negotiation auto

bridge-group 1

!

interface BRI0/2/0

no ip address

encapsulation hdlc

shutdown

!

interface BVI1

ip address 172.18.14.2 255.255.252.0

arp timeout 300

!

no ip forward-protocol nd

!

!

ip http server

ip http authentication local

ip http timeout-policy idle 60 life 86400 requests 10000

!

!

!

control-plane

!

bridge 1 protocol ieee

bridge 1 route ip

Router B#sh spanning-tree summary

Root bridge for: Bridge group 1.

PortFast BPDU Guard is disabled

UplinkFast is disabled

BackboneFast is disabled

Name Blocking Listening Learning Forwarding STP Active

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

Bridge group 1 0 0 0 2 2

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

1 Bridge Group 0 0 0 2 2

Thanks for your help.

Best regards,

Alvin

Hello Alvin,

a loop cannot occur unless you close the two lan interfaces together but STP should take care of this

if you use a fiber connection you may need a media-type command.

do

sh int gi0/1/0

media-type ?

and see the options

check the status of the fiber based links with

sh int gi0/1/0

both devices say they are root bridge for bridge-group 1

Root bridge for: Bridge group 1.

so they are not communicating

Hope to help

Giuseppe

Dear Giuseppe,

Find below the interfaces from both routers:

Router A#sh interfaces

GigabitEthernet0/0 is up, line protocol is up

GigabitEthernet0/1/0 is up, line protocol is up

Hardware is PM-3387, address is 0017.5aa6.d606 (bia 0017.5aa6.d606)

Description: 'Fiber Optics Link'

MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s, link type is autonegotiation, media type is LX

output flow-control is XON, input flow-control is XON

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:04, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 1 packets/sec

24870 packets input, 2138807 bytes, 0 no buffer

Received 73 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

209475 packets output, 18426653 bytes, 0 underruns

0 output errors, 0 collisions, 4 interface resets

0 unknown protocol drops

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 pause output

0 output buffer failures, 0 output buffers swapped out

BVI1 is up, line protocol is up

RouterB#sh interfaces

GigabitEthernet0/0 is up, line protocol is up

GigabitEthernet0/1/0 is up, line protocol is up

Hardware is PM-3387, address is 0015.622e.f3b6 (bia 0015.622e.f3b6)

Description: 'Fiber Optics Connection'

MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s, link type is autonegotiation, media type is LX

output flow-control is XON, input flow-control is XON

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 2000 bits/sec, 4 packets/sec

5 minute output rate 2000 bits/sec, 3 packets/sec

351035 packets input, 29378840 bytes, 0 no buffer

Received 143617 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 0 multicast, 0 pause input

0 input packets with dribble condition detected

35369 packets output, 2863100 bytes, 0 underruns

0 output errors, 0 collisions, 2 interface resets

28 unknown protocol drops

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 pause output

0 output buffer failures, 0 output buffers swapped out

BVI1 is up, line protocol is up

I am able to ping any device in the LAN of Router A from Router B.

The opposite is not possible.

Please advise.

Alvin

Alvin:

Not to distract you from your work, but I am wondering why you find yourself in a situation where you have 2 ethernet interfaces on your router that are cnnected to the same LAN.

Can you also attach a simple diagram to show whats going on?

Thanks

Victor

Dear Victor,

Please find attached the network topology.

As you will see, both LAN A and B are found in the 172.18.12.0/22 subnet.

So, that is why the routers are configured in Bridge mode.

But I am having problems when connecting the LAN interface of Router B. As soon as I connect it to the switch, I am not able to ping it anymore from router A.

Best regards,

Alvin

Alvin:

Thanks.

Have you taken notice of Giuseppe's suggestion? The routers dont seem to be exchanging BPDUs because each is claiming itself as the root bridge.

Victor

Hello Alvin, Victor

collecting facts:

there is a fiber based link working at OSI layer 1 but STP messages are not exchanged.

Alvin:

what type of interface is g0/1/0 is part of some form of etherswitch module ?

in that case the configuration could need to be changed to something like

conf t

vlan 5

name inter-router-vlan

int vlan 5

no ip address

bridge-group 1

int gi0/1/0

switchport

switchport mode access

switchport access vlan 5

if the port is part of an etherswitch the bridge-group command has to be given under the SVI (int vlan 5)

Hope to help

Giuseppe

Dear Guiseppe,

In fact interface g0/1/0 is a Gigabit Ethernet HWIC card (HWIC-1GE-SFP) with a GLC-LH-SM module. For each router it is the same.

Regards,

Alvin

Dear Victor,

So in this typical configuration, should I enable the STP. And which STP should I use?

Which router needs to be the root bridge?

Regards,

Alvin

Hello Alvin,

with your configuration STP is already running in the version IEEE:

the command

bridge 1 protocol ieee

Hope to help

Giuseppe

ok, Guiseppe.

I will continue with the testing.

Regards,

Alvin

Hello Guiseppe,

Hope you are doing fine.

The bridge configuration is working fine but I am encountering another issue that is preventing me from using the routers.

The issue is with Router B's LAN. When I am connecting Router B to the existing switch, I am not able to reach router A and its associated LAN anymore. Timeout occurs when I ping Router A from router B.

When I disconnect Router B from the existing switch, I can then access Router A and its associated LAN.

This seems to be a problem with the existing switch. Can you please explain what can be causing this problem and whether I need to do some modifications in the router configuration.

I did some tests using a standalone switch where I connected Router B and a laptop. Both where accessible from Router A. The problem did not occur.

Regards,

Alvin