Using static routes with redundant links

[krybabie]

I need to setup static routing between 3 routers.

The 1600 router has two links one serial one ethernet.

The ethernet must be primary and the serial must be redundant.

If the ether link fails the serial must immediately come up.

This needs to be done without routing protocols.

The two routers on the other side are a 2611 and a 2621 router.

the 2611 has two ether slots and the 2621 has 100 MB ether slot.

Hope this all makes sense.

regards

malcolm

[paddyxdoyle]

Hi Malcolm,

You can use floating static routes to achieve this.

In a nutshell if you wanted to talk to say network 10.0.0.0 /24 with the ethernet interface as a primary on the 1600 your configuration on the 1600 would be something like

ip route 10.0.0.0 255.255.255.0 ethernet0 <2611_next_hop_IP_address>

ip route 10.0.0.0 255.255.255.0 Serial0 <2621_next_hop_IP_address> 250

There is a good document that explains exactly how to do this here:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800ef7b2.shtml

Good luck

PD

[krybabie]

great just what i needed thanks

[vcjones]

Before you declare the design done, have you considered that the floating static routes will only change if the Ethernet goes down at the link layer. So unless the hub/switch your router is plugged into fails, the Ethernet will continue to be the next hop whether or not the router on the other side of the Ethernet is alive.

There are ways around the limitation, but they make running a routing protocol look trivially easy by comparison (think "ping-based routing").

Good luck and have fun!

Vincent C Jones

[krybabie]

ok i get that - major problem!

How would one go about solving this then? Without using routing protocols.

The people who have these routers do not want routing protocols at all.

Thanks

malcolm

[krybabie]

CHANGE OF PLAN:

Now using two Routers

1 X ????? Router

1 X 2621 12.3 (6a) ISP IOS

need to setup the two one link is serial other ether.

Need a fast ether connection as the ether connection is wireless.

what router would you reccomend maybe a 1700 ? I have a 2611 but it is only 10Mb

also how owuld you route them static?

If using a routing protocol the lines can be balanced 80:20 ether(wireless):serial(leased line)

maybe eigrp with variance would work but how would i set it up

thanks

malcolm

[vcjones]

Q. Need a fast ether connection as the ether connection is wireless.

A. You don't specify what kind of wireless, but keep in mind that IEEE 802.11 wireless limits your throughput to about 50% of the alleged speed, so unless it's a 54Mbps link, a 10 Mbps wire would work just fine.

Q. what router would you reccomend maybe a 1700 ? I have a 2611 but it is only 10Mb

A. A 1721 would allow you to use ping based routing and is a lot cheaper than a 2611 XM. But that would only give you a single FastEthernet port, so you would have to do some "one-armed" routing assuming your incoming traffic is on another LAN.

Q. also how owuld you route them static?

A. With the primary route over Ethernet, I would not waste my time routing them static. There would be no useful redundancy.

Q. If using a routing protocol the lines can be balanced 80:20 ether(wireless):serial(leased line)

maybe eigrp with variance would work but how would i set it up

A. Don't waste your time if the variance is 4 to 1. You will get degraded performance due to serialization delay on the slow link.

Bottom line: If you expect to get improved availability, you will need a mechanism to detect loss of your wireless path. If you run a routing protocol (the overhead is minimal), you can tune it to detect link failure and switch over in a couple of seconds. If you have to use ping based routing, plan on averaging a minute of downtime before the failure is detected and the switch-over implemented.

Also note that you also need to regularly and routinely test the backup link or you will discover it has failed by the time you need it.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

thanks