network is unreachable

[Gus Larsson]

Hello all,
When I try to connect to nameservers outside my local subnet, I receive a message saying "Network is unreachable". Furthermore, when I do this while running tcpdump in another window, no record of the transaction shows up in tcpdump.

I am simply trying to connect using "telnet 128.184.10.133 53". nslookup gives similar results, but I was trying to rule out nslookup as the cause of my problems.

I recently moved this system (HP-UX 11.0 J5600) from a class C to a class B network. I had not been having any problems before doing so. My netmask is 255.255.252.0, my gateway is 128.184.232.1, and my address is 128.184.233.115.

I only have one lan card in my system. ifconfig lan0 reports:
lan0: flags=843
inet 128.184.233.115 netmask fffffc00 broadcast 128.184.235.255.

I seem to be able to connect to the outside world for a few minutes after booting up, but then I lose connectivity.

Any help would be greatly appreciated.

Thank you,
Gus Larsson

[Mark Grant]

Looks remarkably like a routing problem (apart from the worrying few minutes of connectivity you get) any chance o fposting the ouput of "netstat -rn"

[Gus Larsson]

I hope this formats correctly when posted. I'll attach it as a text file in case it doesn't - Gus

/home/gcl/patches> netstat -rn
Routing tables
Dest/Netmask Gateway Flags Use Interface Pmtu
127.0.0.1 127.0.0.1 UH 0 2174 lo0 4136
128.184.233.115 128.184.233.115 UH 0 3211421 lan0 4136
128.184.232.0 128.184.233.115 U 2 0 lan0 1500
127.0.0.0 127.0.0.1 U 0 0 lo0 4136
default 128.184.232.1 UG 0 0 lan0 1500

[Gus Larsson]

Other points for consideration (which I hope don't confuse the issue) are:

1) There are no connectivity issues within my subnet. People in my office area connect to the HP-UX workstation using SSH with no problems.

2) I set my lan card to 10 Mbits, half-duplex, autonegotiate off, because that seemed to be the safest setting based on what I had read in these forums previously. (And this setting worked when I was on my old class C network).

Gus

[Jakes Louw]

Well, it won't hurt to change the the card to another speed setting. Try 10FD, then 100HD, then 100FD.
BTW, what router/switch are you connecting through, and which LAN card model are you using?

[Gus Larsson]

I believe I solved the problem. Maybe what I should have included was that "ping' is filtered/prohibited on the routers and the gateway around here. What I found was that within several minutes of booting, the HP was pinging the gateway and receiving a "prohibited" response. It was always at that point that connections outside the local subnet failed.

I found a post by Zeev Schultz a little while ago (networking/Why HP9000 server always ping the next hop address) that discussed an ndd parameter called "ip_ire_gw_probe" that causes pings to be sent to the gateway periodically. Well, it turns out that if I set that to 0 in the nddconf file and reboot, I don't have any connectivity problems.

I suppose that something on the inside saw that the gateway was down and so didn't bother sending any messages outside of my subnetwork. Just a guess, but I am still connected.

Thanks for the suggestions - I'll assign points momentarily. I wish I could give Zeev an extra 10 points.

Gus

[Jakes Louw]

Thanks for the feedback, Gus. Too many threads on the Forums just "die" without feedback from the initiator.
Great stuff.