[nycphp-talk] multiple gateways and linux

Chalu Kim chalu at
Tue Jun 4 13:03:59 EDT 2002

Why not check out IPROUTE which does fail-over and packet balancing? It is
available on Linux...
Instead of going the circuitous way of HSRP and VRRP or BGP, this is more in
the localized first step to high availability to the intranet.

----- Original Message -----
From: "Jim Suto" <jim at>
To: "NYPHP Talk" <talk at>
Sent: Tuesday, June 04, 2002 12:14 PM
Subject: RE: [nycphp-talk] multiple gateways and linux

> We have 3 T1s, 2 are from Worldcom, one is from Cable & Wireless.  These
> already in place with each provider having its own CISCO router.  If we
> HSRP, we are only going to be using one single router at any time and the
> other one will sit by idle, right?  It's good for redundancy but not for
> maximizing usage of the available bandwidth.  I was thinking of using
> roundrobing DNS for incoming connections to our server using the 3 IPs (1
> from each T1 block).  The outgoing connections could be returned via
> routing perhaps?  And if a gateway is down, use another gateway even if
> will create an assymetrical route?
> In your point (e) if we got two routers for each circuit we would need to
> have 6 routers, do you think the cost would be justified for slightly
> reduced failover risk?  I think the company could live in a pinch even on
> just a single working T1 but it seems like a waste to have all that other
> bandwidth just sitting there unused.  Let me know what you think.
> regards,
> Jim
> -----Original Message-----
> From: Larry Chuon [mailto:LarryC at]
> Sent: Tuesday, June 04, 2002 11:55 AM
> To: NYPHP Talk
> Subject: RE: [nycphp-talk] multiple gateways and linux
> Keep in mind that when you have multiple circuits, you're running into
> complecity with your network design.  Here is a general guideline.
> 1. Are you planning to subscribe the add'l T1 from the same ISP of from a
> different one?
> Same:
> a. Easy to loadbalance (LB) your package both inbound and outbound
> b. You don't require to have a heavy duty router.  This way you can accept
> partial BGP route.  As a result your, hardware requirement is much less.
> c. Use vendor assigned Autonymous System Number (ASN).
> d. If the ISP is down, assuming both T1 are from the same c/o, you're out!
> e. I recommend that you have two separate routers for each circuit.
> Different:
> a. You must apply for you own ASN from ARIN.
> b. Tedious BGP configuration
> c. Setup of LB might be difficult depends on your environment, but not
> impossible
> d. Complete ISP redundancy - due to two separate path in and out
> e. Same as 1e above.
> With the two routers as your gateway, you can configure HSRP/VSRP (depends
> on the vendors).  Essentially, you have two real gateways and one virtual
> one that everyone is pointing to.  When any of the real gateways is down,
> won't affect your connectivity at all.  Linux has something to that affect
> as well.  I don't have experience with it nor do I know what it calls.
> -----Original Message-----
> From: Jim Suto [mailto:jim at]
> Sent: Tuesday, June 04, 2002 11:10 AM
> To: NYPHP Talk
> Subject: [nycphp-talk] multiple gateways and linux
> I am looking for any ideas people might have to maximize the value of
> multiple T1s from different providers and being able to provide redundancy
> and possibly performance gains from having a linux server utilize these
> multiple gateways.  Some ideas I was thinking about:
> 1) enable linux to do dead gateway detection and avoid using a gateway if
> is not up
> 2) enable linux to distribute traffic among the gateways to whichever one
> least busy (this might be a little bit more difficult)
> 3) enable linux to figure out from a list of hosts which gateway would
> connection to a specific host with minimum lag and/or hops
> I guess some shell scripts could accomplish some of these tasks unless
> someone knows a better way?
> regards,
> Jim

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