[cisco-bba] TCP and PPPoE problems with one type of CPE

Mon Jun 25 13:31:30 EDT 2007

We had the same problem back in 2004....

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>Date: Tue, 7 Dec 2004 16:59:59 -0800
>From: Dennis Peng <dpeng at cisco.com>
>To: Clayton Zekelman <clayton at mnsi.net>
>Cc: Arie Vayner <ariev at netvision.net.il>, cisco-bba at puck.nether.net
>Subject: Re: [cisco-bba] LNS issues on a 7301
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>Clayton Zekelman [clayton at mnsi.net] wrote:
> >
> >
> > It may have indirectly been MTU issues.
> >
> > Somewhere along the way, IOS started treating the RADIUS 
> Framed-Compression=Van-Jacobsen-TCP-IP attribute differently.
> >
> > Users who had that attribute set in the RADIUS users file were 
> failing.  Everyone without it (our DEFAULT entry) was fine. It was 
> one of those things we always set during the dialup days, and it 
> never appeared to cause a problem on DSL until we went to 12.3(11)T.
>
>For the archives, this problem exists in 12.3(7)T or later. I've
>opened up a bug on this, CSCsa49007. The release note says:
>
>In IOS releases 12.3(7)T or later, if the command <CmdBold>ip tcp
>header-compression<NoCmdBold> is configured on VPDN virtual-access
>interfaces, TCP traffic will fail to pass. The command may also be
>enabled via the RADIUS Framed-Compression attribute. VJ header
>compression does not have to be negotiated successfully for TCP
>traffic to be affected, it just needs to be configured. The workaround
>is to either remove the <CmdBold>ip tcp header-compression<NoCmdBold>
>command, filter the Framed-Compression attribute using the RADIUS
>Attribute Filtering feature in IOS, or remove the attribute from the
>user's RADIUS profile.
>
>If you have RADIUS profiles with the Framed-Compression set to VJ
>header compression, or would like to use VJ header compression on your
>LNS (eg you are aggregating modem links), please open up a TAC case
>and request that they link the case to this bug. I'd greatly appreciate
>your support in documenting your requests/needs.
>
> > I suspect that somehow when the TCP/IP header was decompressed 
> with VJ, it grew larger and broke things due to the PPPoE packet 
> size limitations.
> >
> > Either way:
> > 12.3(9) - VJ "on" causes no problems.
> > 12.3(11)T - VJ "on" breaks things.
> >
> > I'd rather avoid using ip tcp adjust-mss.  From what I remember 
> in earlier releases, it blocked creation of Virtual-Access 
> Subinterfaces, and caused some performance hits.  I don't know if 
> this is still true. Since my L2TP tunnels come in on an ATM 
> interface, I don't hit the maximum L2TP packet size over Ethernet issue.
>
>TCP adjust-mss is sub-interface capable in 12.3(3) and later
>(CSCea31101). However, anyone using the command on the sub-interface
>should make sure they have the fix for CSCee75569, in 12.3(10) or
>later. Otherwise you will only see TCP adjust-mss sporadically working
>which will cause performance problems.
>
>Dennis
>
> > I opened a TAC case, but the front line guy is still stuck on 
> having me make sure I have "enable vpdn" turned on (despite the 
> fact that the syntax is "vpdn enable" - which of course I must have 
> on to even be able to encounter this problem...<sigh>).
> >
> > I'll send him what I found in the morning.
> >
> >
> > ----- Original Message ---------------
> >
> > Subject: RE: [cisco-bba] LNS issues on a 7301
> >    From: "Arie Vayner" <ariev at netvision.net.il>
> >    Date: Fri, 3 Dec 2004 10:17:00 +0200
> >      To: "Clayton Zekelman" <clayton at MNSi.Net>,
> >           <cisco-bba at puck.nether.net>
> >
> > >You may be hitting some MTU issues?
> > >Try using tcp mss-adjust
> > >
> > >Arie
> > >
> > >-----Original Message-----
> > >From: cisco-bba-bounces at puck.nether.net
> > >[mailto:cisco-bba-bounces at puck.nether.net] On Behalf Of Clayton Zekelman
> > >Sent: Thursday, December 02, 2004 5:19 PM
> > >To: cisco-bba at puck.nether.net
> > >Subject: [cisco-bba] LNS issues on a 7301
> > >
> > >
> > >
> > >We just purchased a new 7301 running 12.3(11)T as an LNS.
> > >
> > >Customers are coming in via L2TP tunnels from a Juniper ERX-1400 on an
> > >ATM OC3c interface.
> > >
> > >We just cut over from a 6400 NRP-1 running 12.2(15)T1, and now some
> > >customers who terminate in PTA's are having connectivity issues.  These
> > >customers were also working fine on a 6400 NRP-1 running 12.3(9) a few
> > >weeks back.
> > >
> > >Currently, it looks as if the customers we tunnel THROUGH the 7301 work
> > >just fine.  Customers terminating are reporting various issues.
> > >Interesting to note that we can ping most of the users from outside our
> > >network just fine.  The ones we can't ping I suspect have ping responses
> > >turned off on their CPE routers.
> > >
> > >As a quick fix, I'm tunneling the users through to another LNS.  Any
> > >suggestions?
> > >
> > >Here's our Virtual Template:
> > >
> > >interface Virtual-Template1
> > >  mtu 1492
> > >  ip unnumbered GigabitEthernet0/0
> > >  no logging event link-status
> > >  load-interval 30
> > >  peer default ip address pool dynamic1
> > >  ppp authentication pap ppp_local
> > >  ppp authorization ppp_local
> > >  ppp ipcp dns 216.8.137.204 216.8.137.203
> > >
> > >
> > >
> > >---
> > >Clayton Zekelman
> > >Managed Network Systems Inc. (MNSi)
> > >344-300 Tecumseh Rd. E.
> > >Windsor, Ontario
> > >N8X 5E8
> > >
> > >tel. 519-985-8410
> > >fax. 519-258-3009
> > >
> > >_______________________________________________
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> > >cisco-bba at puck.nether.net
> > >https://puck.nether.net/mailman/listinfo/cisco-bba
> > >
> > >
> > >
> >
> > _______________________________________________
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> > cisco-bba at puck.nether.net
> > https://puck.nether.net/mailman/listinfo/cisco-bba

---
Clayton Zekelman
Managed Network Systems Inc. (MNSi)
344-300 Tecumseh Rd. E.
Windsor, Ontario
N8X 5E8

tel. 519-985-8410
fax. 519-985-8409        