Re: COM21 is killing me with ARP
Thank you Bryan, I couldn't have said it better. Besides, it is not clear
from the trace provided that all ARPs are coming from the gateway anyway.
vector
----- Original Message -----
From: "Bryan Andersen" <bryan@visi.com>
To: "Patrick Colbeck" <pat.colbeck@bashq.org>; "Sebastiaan"
<S.Breedveld@ITS.TUDelft.NL>; "Vector" <vector@itpsg.com>;
<debian-user@lists.debian.org>
Sent: Thursday, June 14, 2001 2:53 AM
Subject: Re: COM21 is killing me with ARP
> Patrick Colbeck wrote:
> >
> > It really doesnt matter that there is a whole class B address space as
> > you should only get arped when someone om the same class B needs to
> > know your mac address. Once the arping device has your mac address it
> > should cache it so it doesn't have to arp for it again for a long
> > time. All the other people on the calls B shouldn't be trying to find
> > your MAC address as they theoretically should only be talking to your
> > service providers DSLAM.
>
> Actually it does matter. When Joe user turns off their box it
> nolonger can answer requests for it's ethernet adderess. This
> means a bunch of requests for it's arp address. So when
> someone scans the network you get bombarded by arp requests,
> and the caches naturally gets trashed durring this. If you
> know a provider does this you can realy hose up their network
> by bombarding them with random addresses in their network space.
> To keep from having this trash a network the router really
> needs to have enough cache entries to store all hosts on the
> network. Many routers just can't handle that for a class B
> network. They really should break their network up into
> class Cs.
>
> > It sounds like somebody has screwed up at the service provider
> > configuring their routers they have probably:-
> >
> > i) Configured a really small arp cache timeout value so the service
> > provider router is permanatly having to re arp for the mac
> > addresses of all the DSL modems or
> >
> > ii) Configured a static route via a broadcast interface (eg etherent)
> > on the cental router. This is a really bad thing as instead of just
> > arping for the next hop address the router will arp every time it
> > needs to send a packet to any address on the network the route is for
> > to try and determine the gateway to that address. This is a really
> > good way to crucify network performance , static routes pointing at
> > interfaces rather than next hop addresses should only be used on point
> > t point networks (leased line etc).
>
> --
> | Bryan Andersen | bryan@visi.com | http://www.nerdvest.com |
> | Buzzwords are like annoying little flies that deserve to be swatted. |
> | -Bryan Andersen |
>
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