RE: [fw-wiz] IPSEC over load-shared T1s (per packet)
From: R. DuFresne (dufresne_at_sysinfo.com)
To: Ben Nagy <email@example.com> Date: Fri, 19 Sep 2003 11:32:11 -0400 (EDT)
I might be reading Ben wrong, but, I get the impression he is talking
about session concerency? A 'sticky' bit in the load balancer end, such
that a session started and sent via one t1 remains directed through that
path for the remainder of the session?
On Thu, 18 Sep 2003, Ben Nagy wrote:
> ObBOFH: One of the T1 RJ connectors must be dirty, which is causing packet
> corruption. Give both the telco jacks a good clean (licking them works well)
> and see if that fixes the problem. 
> Seriously, I do have a theory ;)
> Does this routing guarantee to preserve sequencing?
> If it's really as you described (packets send one for one via alternate
> links) then you have some potential problems brewing, I think.
> TCP will "work things out" when packets arrive out of sequence, but with
> IPSec it's left up to the implementation. One security concern with most
> crypto things is replay protection. IPSec addresses this by using a
> mandatory sequence number in the ESP header. The receiveing IPSec doesn't
> _have_ to take any notice, but most do. If your receiving IPSec has enabled
> replay protection then if one link is going faster half the packets are
> going to get dropped (sequence number < current).
> This would make your tunneled protocol (say TCP) do the retransission thing,
> so it would work itself out eventually, but the speed would indeed suffer
> See if you can convince your router to preserve "IP flows" and use the two
> links in a more sensible manner. That might help.
> Best of luck,
> PS: Let us know when you work it out? This is an interesting one.
>  The RJ's are live, for non-network-engineer types. Not enough to kill
> you, but it hurts. :)
> > -----Original Message-----
> > From: firstname.lastname@example.org
> > [mailto:email@example.com] On Behalf
> > Of TSimons@Delphi-Tech.com
> > Sent: Thursday, September 18, 2003 3:38 AM
> > To: firstname.lastname@example.org
> > Hello All
> > Recently we doubled our internet bandwith to two T1s from the
> > same provider
> > that terminate on in the same router on the NOC side.
> > We setup IP LOAD-SHARING PER-PACKET on each of the serial
> > links on both
> > sides (NOC and Us) in order to get an aggregate 3.0mbit.
> > PER-PACKET routing
> > alternates usage of the T1s, one for one...
> > Since then, VPN performance has taken a dive. Sniffing out
> > traffic, ESP
> > packets are sent 3-4 times before they can be properly decrypted.
> > Someone along the way said that using PER-PACKET routing
> > changes the CRC
> > value of the packets. Is this correct, has anyone else seen
> > this issue? I
> > can't see how the CRC is changed, the hop count isn't
> > changing, the lines
> > are identical, and they terminate in the same router, so the
> > last hop is the
> > F0/0 interface of the router before getting to the firewall.
> > Thanks,
> > ~Todd
> > __________________________________
> > Todd M. Simons
> > Senior MIS Engineer
> > Dell Tier 1 PA Technician
> > Delphi Technology, Inc.
> > New Brunswick, NJ
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