Sam,
You've gotten several good replies about using DHCP super-scopes and
multiple HSRP groups. While these ideas will certainly work, there's a far
simpler approach.
Your original question was whether or not using HSRP allowed you to use the
T1 connected to the secondary router. The answer is yes, but its up to the
primary router to get the packets to the secondary, not the workstations.
>From the workstations perspective, there is only 1 router. This is the
benefit and, also, the downside of HSRP. All of the games with DHCP
superscopes and multiple HSRP groups are needed to get around the fact that
HSRP hides the fact that there are multiple routers from the end stations.
This is by design.
IMO, its far simpler to let the end stations continue to believe there's
only 1 router and then let the primary router send packets to whichever
router has the best route to the destination. All that is necessary to
accomplish this magic is to have your routers peer via BGP with your
provider and each other. Assuming that you have different ISP's, you will
naturally get some load-sharing. Even with 2 connections to the same ISP
there are lots of BGP settings you can tweak to get load-sharing however
your policies dictate. ("Internet Routing Architectures" by Sam Halabi is
the BGP bible)
The way this would work in practice is simple:
1) WS sends packets to its DG (aka the primary router)
2) Primary router either has the best route and sends to upstream provider
or secondary router has best route and primary forwards to secondary,
secondary forwards to upstream ISP.
Normally, the primary router would send an ICMP redirect to the WS telling
it to send packets directly to the secondary since the secondary has the
better route. However, enabling HSRP disables the sending of ICMP
redirects, so packets will continue to go first to the primary, and then to
the secondary for routes preferred through the secondary. This will put
excess traffic on the primary's LAN interface, but with only a couple of
T1's worth of traffic, this should not cause any problems.
One thing you will want to do is to place the command 'ip route-cache
same-interface' on the primary routers LAN interface. Otherwise, all
packets in and out the same interface would be process switched and spike
the routers CPU.
By using this method you leve the complexity to the routers and keep the WS
simple.
HTH,
Kent
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
Sam Sneed
Sent: Friday, June 29, 2001 12:58 PM
To: [EMAIL PROTECTED]
Subject: HSRP [7:10428]
I was doing a little research on HSRP and had a question for anyone who has
configured it. I read the whole RFC 2281 and could not find my answer there.
If you have two routers running HSRP with T1 lines to the internet, 1 is the
standby and one is the active. Does all traffic only go through the active
at all times unless it dies? If so isn't it a waste not ever utilizing the
T1 line thats on standby (of course until the active fails)?
If bandwidth exceeded 1.5MB would the second router kick in to share the
load or would it totally take over?
With these 2 routers acting as a single virtual router would throughput
ever be able to exceed 1.54 MB assuming each has its own T1 connection?
thanks
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=10738&t=10428
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