Fw: [past-noc] Weird network config problem

[Brian Chee]

Thought you folks might be interested......this particular bug will really
drop a monkey wrench into the works if you're doing layer 4 load
balancing.....so good thing to beware of on multi-homed boxes.

/brian chee

University of Hawaii ICS Dept
Advanced Network Computing Lab
1680 East West Road, POST rm 311
Honolulu, HI  96822
808-956-5797 voice, 808-956-5175 fax

----- Original Message -----
From: "Bill Burge" <b.burge at mindspring.com>
To: "Past-Noc (E-mail)" <past-noc at interop.net>
Sent: Monday, October 22, 2001 5:53 AM
Subject: RE: [past-noc] Weird network config problem


> I've seen linux hosts with two interfaces answer arp's on int A for the
address of int B.
>
> Main reason I stopped using it in dual-homed situations...  Drove things
like my Alteons nuts...
>
> It's been this way for some time, I found a reference to it in a kernel
programmers board about two years ago, and it was na old post.
>
> Here's some light reading:
>
> http://www.uwsg.iu.edu/hypermail/linux/net/9810.0/0094.html
> http://www.beowulf.org/listarchives/linux-eepro100/1999/12/0005.html
>
> Bill Burge
>
> *********** REPLY SEPARATOR  ***********
>
> On 10/22/2001 at 9:39 AM Steve Hultquist wrote:
>
> >Both machines are Unix. NS is a BSD box with some weird software on it.
> >terk
> >is a Linux box. Both are Intel.
> >
> >ssh
> >
> >-----Original Message-----
> >From: Ron Pashby [mailto:Ron at pashby.org]
> >Sent: Monday, October 22, 2001 8:06 AM
> >Cc: Past-Noc (E-mail)
> >Subject: Re: [past-noc] Weird network config problem
> >
> >
> >What kind of machine is terk?
> >
> >Steve Hultquist wrote:
> >
> >> This one has me stumped, so I thought I would submit it to brighter
minds
> >> than my own... While there are some problems here that we're in the
> >process
> >> of fixing, it is the symptoms that I'd like to better understand.
> >>
> >> We have a network (10.10.200/24) with a bunch of machines on it. One of
> >the
> >> machines is a Web accellerator (NS) that proxys for Web servers, but
acts
> >as
> >> a bridge on the network. One of the machines (terk) that used to be
> >behind
> >it
> >> (10.10.200.239) I moved in front of it today. Now, here's the weird
part:
> >>
> >> NS is plugged into port 7 on the front-end switch (Summit) and port 2:9
> >on
> >> the backend switch (Alpine)
> >> terk is plugged into port 40 on the front-end switch and into a
different
> >> VLAN on the back-end (port 2:16)
> >> the Summit sees the proper MAC for terk, but... sees the MAC on port
7!!!
> >> the Alpine sees the proper MAC, but... on port 2:9!!!
> >> port 40 on the Summit shows *no MAC* in the forwarding database!
> >>
> >> BUT, traffic still gets to terk. Even when terk's backend interface is
> >> downed.
> >>
> >> How is that possible?!?!?
> >> ssh
> >>
> >> -------------------------------------------------------------  (Summit
> >Common
> >> VLAN)
> >>     |   port 7                          |    port 40
> >>     |                                   |
> >>    NS                                 terk
> >>     |                                   |
> >>     |   port 2:9                        |   port 2:16
> >> ---------------- Alpine LB VLAN      --------------------- (Alpine
> >BackEnd
> >> VLAN)
>
>
>