[nsp] Bridging DSL to 7206

From: Mark E. Mallett (mem@mv.mv.com)
Date: Fri Sep 08 2000 - 16:51:28 EDT


I've been tearing out some small amount of remaining hair here and
wonder if anyone has some thoughts...

Using a 7206 and a PA-A3-T3 to terminate a backhaul DS3 loop from a
CLEC who is providing DSL connections. The 7206 is running
12.1(1a)T1. The relevant config is:

bridge irb
!
interface ATM2/0.15 multipoint
 description PVC to CLEC
 pvc clec 15/799
  encapsulation aal5snap
 !
 bridge-group 20
 bridge-group 20 spanning disabled # or not, have tried both
 bridge-group 20 subscriber-loop-control # or not, have tried both
!
interface BVI20
 description CLEC DSL customer group
 ip address A.B.C.1 255.255.254.0 # a /23 ... have also tried a /24
 ip helper-address D.E.F.G
 ip route-cache same-interface # or not
 no ip mroute-cache
 exit
!
bridge 20 protocol ieee
bridge 20 subscriber-policy 20 # or not
bridge 20 route ip
!
end

We've installed a DSL line and are testing it; we've had various
systems and operating systems on it. A good description of the problem
can be had with our experience with a linux box on the end of the
DSL line.

As a first step, I hardwire an IP address on the linux box.

If I try to ping the router (at the other end of the DSL line) from
the linux box, it fails. However the linux box *does* gain the ARP
address for that router, meaning that it does get the MAC level address
from the link. (I can also see the arp request and response via tcpdump.)

If I try to ping the linux box from the router, there is no response,
and the cisco does NOT obtain the arp address from the linux box. I
can see the cisco sending ARP queries in order to obtain the MAC level
address for the linux box. The tcpdump on the linux box does NOT show
any arp queries arriving.

If I go to the cisco and hardwire the arp info for the linux box's IP
address, I now have connectivity. I can ping between the router and
the linux box, and indeed out to the rest of the world from the linux
box.

If I attempt to make DHCP requests from the linux box, they never arrive
at the cisco (at least not in any way that I can find -- they don't
show up in packet log, and the packet counts do not go up, nor are they
forwarded to the helper address).

Using tcpdump on the linux box, I can see the DHCP requests going out the
ethernet interface, and nothing coming back.

It almost looks like the CLEC is blocking layer 2 broadcast traffic,
but (a) they say they are not and (b) they have other customers. So
I'm inclined to believe I've done something wrong. I've read
documentation until the pixels are wearing off onto my eyeballs, and
have tried an enormous amount of tweaks.

Any clues?

-mm-

-- 
Mark E. Mallett                  |    http://www.mv.com/users/mem/
MV Communications, Inc.          |    http://www.mv.com/
NH Internet Access since 1991    |    (603) 629-0000 / FAX: 629-0049



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