Yes, ISPs are always multihomed, but multihomed does not mean
multi-routed for every single route path. That’s why whenever you get one of
these disputes, certain routes are cut off until the dispute is resolved. When
you use application proxies (or DNS remapping) to re-route, you’re simply
working around the broken IP link but the link is still broken.
I use to administrate a network where we acted as a smaller
ISP. When we had BGP routes flap between two separate uplinks, it could take
several minutes or even an hour to come back up.
George
From: Kevin McArthur
[mailto:kevin@stormtide.ca]
Sent: Friday, October 31, 2008 5:11 PM
To: George Ou
Cc: 'Barry Gold'; 'NNSquad'
Subject: Re: [ NNSquad ] Re: Peering dispute cuts off
Sprint<->Cogent Internet traffic
George,
In this case however, we're talking major carriers, which have many many peers
(massively multihomed). There are multiple routes around, as evidenced by the
fact that people are using proxying services to get around the damage at the
application layer.
As for BGP propagation, if its following the RFC then the routes are already
advertised and before the peering agreement broke down, they just happened to
be a shorter path. Once that peer dies, it should fall back to the longer paths
in near real-time. (within moments, as soon as the bad route stops advertising
(which it cant do if it cant reach the other end)) This is a core routing
principle of the internet, and how it is supposed to be tolerant to attacks on
infrastructure -- If this mechanism isn't working, then we have some serious
resiliency problems on critical backbones.
You would have to do something special to stop BGP from rerouting -- like, for
example, falsely advertising a route that doesn't work while making it appear
closer than the alternatives. You could also theoretically block the remaining
peers from advertising routes to that network, but again, that would be a
massive net neutrality violation as they would be actively blocking a pathway,
and not simply just not peering. Essentially, saying if I don't want to peer
with you, no one else can either.
There's more going on here....
Kevin McArthur
George Ou wrote:
There's no violation of any RFCs here, it's a peering dispute which is quite
common on the Internet.
It's a long running myth that routes are automatically rerouted on the
Internet. Unless one of the two end-points is dual-homed with 2 completely
separate ISPs configured for BGP (or DNS remapping), any break in the route
means a disconnection between the two points. Even when BGP does exist, it
takes some time for the routes to propagate so there's always some outage
for a period of time when there's a break in the link.
George
-----Original Message-----
From: nnsquad-bounces+george_ou=lanarchitect.net@nnsquad.org
[mailto:nnsquad-bounces+george_ou=lanarchitect.net@nnsquad.org] On Behalf Of
Barry Gold
Sent: Friday, October 31, 2008 1:38 PM
To: NNSquad
Subject: [ NNSquad ] Re: Peering dispute cuts off Sprint<->Cogent Internet
traffic
From: Ed Jankiewicz <edward.jankiewicz@sri.com>
Subject: Total Filtering
As many news organizations are now reporting, Sprint-Nextel (Embarq) has
decided to sever its Internet connection with Cogent, another Internet
service provider. This action has caused a "hole" or "rip" in the
internet, meaning that Sprint-Nextel (Embarq) and Cogent customers may
find they cannot access resources hosted by the other company's
customers. Similar standoffs have occurred in the past, and usually one
company backs down after a few days, but no one can predict what will
happen in this case.
OK, so what has happened to the "treats censorship as damage and routes
around it" Internet? Even if Embarq and Cogent are no longer talking to
each other, the routers should be automatically finding routes via other
carriers and sending the packets -- around Robin Hood's barn if
necessary, but the Internet is supposed to be _robust_. Jon Postel
designed it that way -- I've read the RFCs. That's what ARPA specified
when they paid for the development of first the ARPANet and later the
Internet -- and what NSF paid for when they branched off NSFNet and
allowed commercial traffic.
Are these guys programming their routers to just drop packets with
certain destination IP addresses, instead of finding the shortest
available route?
I'm beginning to think that Congress (or perhaps an international body
similar to the WTO) should make the core RFCs (IP, TCP, BGP, FTP, HTTP,
SMTP, and RFC 822) have the force of law. And anybody who violates
those protocols should be fined and/or have their connections turned off.
--
Kevin McArthur
StormTide Digital Studios Inc.
Author of the recently published book, "Pro PHP"
http://www.stormtide.ca