Dynamic routing

[Greg Hall]

On my D230, when a route goes down, my system builds an (unwanted) dynamic route ;
I then have to delete same before the real route can resume. Is there a way of stopping the system from building such dynamic routes (eg ; UGHD)

[Stefan Farrelly]

This is indeed a tricky sort of problem. Thing to look for;
1. ensure yourenot running gated (see /etc/rc.config.d/netconf)
2. Add static routes into the same netconf file instead of letting dynamic routes be established, this way the static routes will stay on your HP, even if the route actually drops.
3. If you do get dynamic routes being added flush the entire routing table with route -f and then add in static ones using route add.

[John Palmer · Accepted solution]

This problem is caused by the router(s) issuing ICMP redirect messages. Have a look at this previous thread:-

http://my1.itrc.hp.com/cm/QuestionAnswer/1,1150,0x7e4b49c5ae73d4118fef0090279cd0f9,00.html

[Anthony deRito]

Denis, as John has indicated, your routing tables are receiveing ICMP redirect messages from your routers. When the primary gateway for a device is not longer able to pass the packet on to its destination, it will send an ICMP redirect message to your server suggesting another possible route to use. If there is another router on your network that may be a candidate for the route, your routing tables will reflect that new route.

You have a few choices here. You can turn off ICMP redirects on your routers or handle the change in the tables yourself either automatically or manually with some notification. Turning off ICMP redirects has its negative points as you can imagine. "Learning" routes is just what routers and level 3 switches are intended to do.

What I did was to write a script that will detect when a dynamic change is made in the routing table. This is evident by the "M" flag set when you run netstat -nr. Then I take action based on that notification.

Tony

[Edward D. Herring]

What type routers are you using?
Also, what routing protocol.

[Greg Hall]

John/Anthony,
Thanks for helping me understand this; particularly the previous discussion/link. One new awk script on its way ... cheers