Re: COM21 is killing me with ARP
Thanks for all the info everybody gave. It seems that I am powerless to
undertake some action. I have already contacted my cable company, but I
have heard that it is a real mess there, so the chance that it will be
solved one day lies between a quarter and 0.25.
Thanks,
Sebastiaan
On Thu, 14 Jun 2001, Vector wrote:
> 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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