I am working on something in the lab, and I was wondering...

I have two HDLC serial connections that I am bridging together...

bridge irb
!
interface Serial0
 no ip address
 clockrate 56000
 bridge-group 1
!
interface Serial1
 no ip address
 clockrate 56000
 bridge-group 1
!
interface BVI1
 ip address 10.254.39.227 255.255.255.248
!
bridge 1 protocol ieee
bridge 1 bridge ip              < - this command has been entered but 
doesn't show up in the config


The other two routers are at .225 and .226

When I ping from 226 to 227, I get:

00:35:38: IP: tableid=0, s=10.254.39.227 (local), d=10.254.39.226 (BVI1), 
routed  via RIB
00:35:38: IP: s=10.254.39.227 (local), d=10.254.39.226 (BVI1), len 100, 
sending 00:35:38: IP: s=10.254.39.227 (local), d=10.254.39.226 (BVI1), len 
100, encapsulation failed

Why?



Jonathan

Hi Jonathan,

> 00:35:38: IP: tableid=0, s=10.254.39.227 (local), d=10.254.39.226 (BVI1), 
> routed  via RIB
> 00:35:38: IP: s=10.254.39.227 (local), d=10.254.39.226 (BVI1), len 100, 
> sending 00:35:38: IP: s=10.254.39.227 (local), d=10.254.39.226 (BVI1), len 
> 100, encapsulation failed
> 
> Why?

Bridging is Layer 2, IP is Layer 3. So you have no path for Layer 3 
between the devices, thats why your encapsulation failed.
It goes back to near the beginning of your post -

> !
> bridge 1 protocol ieee
> bridge 1 bridge ip              < - this command has been entered but 
> doesn't show up in the config

Thats because a Bridge group only Bridges by default. You are probably
thinking of -

> bridge 1 protocol ieee
> bridge 1 route ip
                    ^^^^^^^^
Meaning all data EXCEPT IP would be bridged on that link.
So your problem is that IP addressing is irrelevant at the frame 
(bridge) level and routing of IP addressing does not exist.

A BVI allows you to attach Layer 3 properties to a Layer 2 entity and 
nothing more. You still need to tell the Router what to do with Layer 
3 traffic on that interface (otherwise why are you adding IP 
addressing to it)?.

Consider this as an example that may help -
I had one site that had a Router connecting the local Ethernet segment
to a 512Kb/s Frame-Relay WAN link. They needed MAC filtering to be 
applied, however because a Router Ethernet interface normally operates
in Layer 3 mode, a MAC ACL is not valid. If I BRIDGED the Ethernet to 
the WAN link, then effectively the LAN would be slowed from 10Mb to 
the speed of the Frame-Relay WAN (512Kb/s), so I converted the 
Ethernet to Bridged mode, Bridged it to a BVI, meaning the Ethernet 
was in Layer 2 mode, ran at Ethernet speed, and so could take the MAC 
ACL, and the BVI allowed me to ROUTE off that interface, meaning the 
Ethernet was not restricted by the WAN link speed.


Cheers...............pk.
-- 
Peter from Auckland.