netstat

[John Jimenez]

I was just reading someone elses thread. I seldom have network issues, so I never noticed this. 3 of my servers showed U, UH (Host), UG (I assume gateway). But in one of my servers I am getting a UGH. gateway/host?

10.0.0.2 10.0.0.2 UH 0 lan0 4136
172.31.252.2 10.0.0.254 UGH 0 lan0 0
10.0.0.0 10.0.0.2 U 2 lan0 1500
default 10.0.0.1 UG 0 lan0 0

[James R. Ferguson]

Hi John:

Yes, "G" = gateway. See the 'netstat(1)' manpages.

Regards!

...JRF...

[John Jimenez]

Thanks James. my question was more on what UGH was not UG? My gateway is 10.0.0.1, but I have no idea what 172.31.252.2 (UGH) is?

[John Jimenez]

Hmmm.... I just did the command again and it 172.31.252.2 did not show up this time... strange.

[Yang Qin_1]

The U flag indicates that the route is up; the G flag indicates that the route is to a gateway. The H flag indicates that the destination is a fully qualified host address, rather than a network.

Yang

[John Jimenez]

Thanks. that 172.31.252.2 showed up the first time issued the command, but has never shown up again.

[Yang Qin_1]

172.31.252.2 is a destination network. Somebody or application(?) forwarded (maybe) packets to it through 10.0.0.254

It is not possible? anyway, when transfer completed, you may not see it again. Or say you are lucky to type netstat at the right moment to capture it.

Yang

[John Jimenez]

I guess it did.

[John Jimenez]

Since I cannot reproduce this output, I am closting this thread. Thanks again.

[rick jones]

H means it was an explicit host route to 172.31.252.2 via 10.0.0.254. The PMTU field being 0 suggests it was "timed-out" and may have been added by Path MTU discovery - communicating to that host found a path that had an MTU less than 1500 bytes by the look of your routing table shown in the initial post.

If you try to ping that remote IP with a large packet size, you _might_ be able to reproduce the entry. That or do something like a netperf TCP_STREAM test to it or a large FTP or something.