Route table question

[RobDunkley]

I posted this in another group that was probably the wrong place so I thought I'd post it again.

We have Cisco 1921 routers that a provider is using for MPLS. They have it configured so that all internet trafic is passed to an internal ip address that is our proxy server. However, they are pushing all of the routing rules down to the workstation which is causing the local route tables to grow to be massive in a very short time.

For example, the second I ping a website, the ip address is resolved and then the route is added for the source ip address with the default gateway of the proxy server.

Is this normal? I would have thought that all the rules would have been handled by the router and let it keep the table entries.

Thanks for any help you can offer.

[Giuseppe Larosa]

Hello Rob,

>> For example, the second I ping a website, the ip address is resolved and then the route is added for the source ip address with the default gateway of the proxy server.

>> they are pushing all of the routing rules down to the workstation which is causing the local route tables to grow to be massive in a very short time.

This might be the effect of ICMP redirect messages sent from network device to PC indicating the proxy server as the gateway for each required destination

For the effects and workaround on PC side you can see

http://www.xnews.ro/QWDisable_ICMP_Redirect.htm

For an explanation on ICMP redirect on cisco routers you can read

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094702.shtml

For disabling ICMP redirects on the router internal LAN interface

configure t

interface type x/y

no ip redirects

All the PC workstations should have the proxy-server as their default gateway and not the Cisco router.

WARNING: without knowledge of your network topology it is not possible to understand if your internet access will still work after disabling ICMP redirects on the router. It should work but it is wise to consider all possibilities.

However, the first link provides a way to make a windows PC to ignore ICMP redirects and can be used to verify if the filling of the routing table on the host is caused by ICMP redirects  ( likely)

If you can install a wireshark protocol analyzer on a PC you can also capture the ICMP redirect messages and you can find out what is the device sending them to your PC.

Hope to help

Giuseppe