Problem Routing SLES 11 SP3

i have a strange routing problem under SLES 11 SP3.

I have the following network interface settings:
eth1 Link encap:Ethernet HWaddr AC:16:2D:6F:7E:F1
inet addr: Bcast: Mask:
RX packets:1952841 errors:0 dropped:5520 overruns:0 frame:0
TX packets:587477 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:522637737 (498.4 Mb) TX bytes:793376827 (756.6 Mb)

And these Routing Table:
Destination Gateway Genmask Flags Metric Ref Use Iface UG 0 0 0 eth1 U 0 0 0 lo U 0 0 0 eth1 U 0 0 0 eth1

The is our default Gateway for the whole network.
There are more than 500 Hosts using these Gateway.

Only on these Server SLES Server I have a problem to reach some networks.
Some IPs work, some doesnt work.

Here an example traceroute to an IP Addresses in our Subnet

Working correct:
traceroute to (, 30 hops max, 40 byte packets using UDP
1 ( 0.359 ms 0.116 ms 0.088 ms
2 ( 2.545 ms * *

Not Working:
traceroute to (, 30 hops max, 40 byte packets using UD P
1 * * *
2 * * *
3 * * *
4 * * *
5 * * *
6 * * *
7 * * *
8 * * *

Sometimes some hots work, sometimes they don`t.

I also try to use another network interface.

I don’t have any idea what causes these problem.
Please help me! :wink:


Ein ähnliches Problem hatten wir unter einem CENTOS Server.

Da hat das hier geholfen.


Controls IP packet forwarding

net.ipv4.ip_forward = 1

Unter SLES mit

Controls IP packet forwarding

net.ipv4.conf.all.forwarding = 1

ändert sich aber nichts am Verhalten

Hi Jörg,

have you had a look at the corresponding tcpdump / wireshark output, to see if your box is sending proper ICMP requests to the correct gateway (check the destination MAC of the ICMP requests).

And you may want to take a look at the ARP table of the server, to check for stray entries (whereever these may have come from - if they’re there, we’ll try to find out :wink: )