[97225] in RedHat Linux List
Routing problem w/ 2.1.126.
daemon@ATHENA.MIT.EDU (Damon T. Miller)
Mon Nov 2 01:19:14 1998
From: "Damon T. Miller" <dtm@harmonixmusic.com>
To: <redhat-list@redhat.com>
Date: Mon, 2 Nov 1998 01:16:27 -0000
Resent-From: redhat-list@redhat.com
Reply-To: redhat-list@redhat.com
Hello. My organization recently acquired DSL service and I'm not trying to
prepare a Linux router to act as a packet-filter for the network. I am
having difficulty with establishing connectivity between the two subnets I
have created (both mask=255.255.255.224, effectively diving the 64 IP's into
two groups of 32.) More specifically, I am having trouble with ARP across
the segments.
At this point, I can ping out from the Linux box to the internet. I can
reach the Linux box from the internet. Additionally, I can reach both of
its interfaces from the local network and I can reach the client machines
from the Linux machine. However, the client machines cannot ping out
successfully (to internet hosts).
The actual root of the problem is this: The Linux machine is not replying
to the gateway's (provided by the ISP--not part of our hardware) ARP who-has
requests. This means that the ICMP echo-request packets are leaving the
client machines, forwarding across the Linux router's interfaces, and going
through the ISP's router to reach their destination. That destination host
(any--I have tcpdump'ed on a remote host and watched it happen) then
replies, and the echo-reply gets all the way to our gateway, at which point
it (the ISP's router) requests the client machine's MAC address (ARP), to
complete the send. Unfortunately, our Linux ignores this request, and the
packet is lost.
I have verified all of this by sniffing on both remote hosts and both of our
Linux router's interfaces.
So, does anybody have any ideas? Is there something I need to enable on the
Linux router to make it respond to remote hosts' requests for MAC addresses
behind (i.e. part of its LAN interface)? Or maybe it should simply forward
those requests to its LAN interface at which point the client machine will
answer? So maybe it's the routing table?
Anyway, I'd really appreciate any help, as I'd love to get our new DSL
connection working!
Thanks so much,
Damon T. Miller
Harmonix Music Systems, Inc.
Cambridge, MA 02139
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