Dynamic ARP entries, when GATED is not running

[Shariq Siddiqui]

Hi,
On our HP9000 (OS ver 10.X) we have disabled GATED from running. We power cycled our HP server and then when I issue netstat -rnv, it displays whole bunch of arp entries with UHGD status. If GATED is not running how and why is the HP system receiving these??? Any help is appreciated.

Shariq

[Craig Gilmore · Accepted solution]

The routing entry listed with flags set to UGHD is not created by gated. The "D" that the man page documents as "Dynamic" is better documented as "redirected".

What has happened is that the route used to reach the IP address listed in the entry that has the UGHD flags has been redirected to use the gateway specified in the UGHD entry. Check the router or gateway that would normally be used to reach the IP address. For some reason, that device told the system to use a different route. The HP-UX system being a good network neighbor must accept/act upon the receipt of the redirect. This packet is received and the routing table is updated with the info.

The problem is not your system, but rather the device on the network.

[rick jones]

In addition to a redirect, you can get those D entries from a PathMTU "hit" - if you see D entries with a PTMU listed lower than the link-local MTU they came from PathMTU discovery, and the intermediate device was doing what it was supposed to do. We asked it to tell us if the size of the pipe between us and the remote system(s) was smaller than our own pipe (in terms of maximum packet size). Those D entries will also have a gateway IP address the same as our original gateway IP address.

A classic redirect implies that the system we thought to use as a gateway felt that there was a better way to get there - such entries will have a different gateway IP address.