[76853] in North American Network Operators' Group
Re: BGP 011: multiple sessions with upstreams
daemon@ATHENA.MIT.EDU (Joe Abley)
Sat Jan 1 11:20:13 2005
In-Reply-To: <Pine.LNX.4.44.0412311524320.19198-100000@a.mx.ict1.everquick.net>
Cc: nanog@merit.edu
From: Joe Abley <jabley@isc.org>
Date: Sat, 1 Jan 2005 11:19:15 -0500
To: "Edward B. Dreger" <eddy+public+spam@noc.everquick.net>
Errors-To: owner-nanog-outgoing@merit.edu
On 31 Dec 2004, at 11:01, Edward B. Dreger wrote:
> I'm trying to persuade them that two provider/customer BGP sessions is
> a
> good thing,
The obvious reason for this might be explained along the lines of "your
router can reach two of our routers. We'd like a BGP session to each so
that we can take our routers down for maintenance when we feel like it,
without causing routes to be withdrawn". If this doesn't gel with their
policy, and you care about it, find a new ISP (but see below).
> and NEXT_HOP set to the HSRP-managed IP address would allow
> them to steer customer traffic.
I've made efforts to set this kind of thing up before (not at ISC), and
in hindsight I wish I hadn't bothered. It was an unconventional
configuration from the provider's perspective that was not preserved
across provider router upgrades and configuration cleanups, and it
opened us up to yet another failure mode (that of HSRP breakage, which
is most definitely not unknown on many releases of IOS).
If you suffer unplanned outages so often that HSRP is going to make a
noticeable difference, then it's probably a good idea to deal with
whatever is causing the unplanned outages (unreliable telco, squirrels
chewing through cables, poorly-sized UPSes, crimp-happy PBX monkeys).
If you're trying to protect against planned outages, then gracefully
admin-downing the BGP sessions on the router which has impending
maintenance (leaving BGP sessions to other router(s) up and running)
might accomplish the same graceful failover that you're trying to use
HSRP for.
> Their argument is that one can "get
> extra bandwidth" with two BGP sessions, and that HSRP prevents that.
> I've pointed out that equal-cost multipath BGP is far from default
> behavior, and that one can "get extra bandwidth" even without two BGP
> sessions.
An extra BGP session will not magically give you more bandwidth. An
extra circuit will not-so-magically give you more bandwidth, although
often not as much as you think.
> Am I missing something?
For your provider, supporting pur-laine, standard-configuration
customers is cheaper than supporting customers where each has their own
special-case setup. Supporting a network of routers where the protocols
and configuration is consistent is also easier (and hence cheaper) than
a network where each router has special, exciting new config bits found
nowhere else.
Your choices may be:
1. Pay a premium to deal with an ISP who can really afford to support
special-case customers;
2. Pay a cheaper price, and deal with reduced support and spontaneous
mystery outages as engineers not familiar with your particular
arrangement make general changes to their network;
3. Accept the standard setup, pay a cheaper price and get reasonable
support.
Joe
