I am trying to setup GRE between two CentOS 4.5 boxes. I have tried
several variations of what's listed below, but none of them work.
box1:
modprobe ip_gre
ip link set gre0 up
ip tunnel add gretun mode gre local 66.1.1.161 remote 66.1.2.161 ttl 20 dev
eth0
ip addr add dev gretun 10.253.253.1 peer 10.253.253.2/24
ip link set dev gretun up
ip route add 10.2.0.0/16 via 10.253.253.2
box2:
modprobe ip_gre
ip link set gre0 up
ip tunnel add gretun mode gre local 66.1.2.161 remote 66.1.1.161 ttl 20 dev
eth0
ip addr add dev gretun 10.253.253.2 peer 10.253.253.1/24
ip link set dev gretun up
ip route add 10.1.0.0/16 via 10.253.253.1
tcpdump shows NO rx or tx traffic from either box that isn't ARP or SSH.
It's as if it's not even trying to bring the tunnel up. I'm a Cisco guy,
so I'm lost with my show commands.
The other variations I've tried consist mostly of trying different
combinations of on-net (in the same subnet as eth0 and even the same address
as eth0) and off-net (various combinations of loopback /24 and /32 addresses
in separate 10 space) on the 'ip addr add dev gretun' statements. But the
above example is what *should* work on a Cisco, I think. It's been a
while.
How do I troubleshoot this? This is all I've got so far:
root@den1tun01:/home/root $ ip link
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP> mtu 8800 qdisc pfifo_fast qlen 1000
link/ether 00:19:b9:dd:ff:d9 brd ff:ff:ff:ff:ff:ff
3: eth0.2: <BROADCAST,MULTICAST,UP> mtu 8800 qdisc noqueue
link/ether 00:19:b9:dd:ff:d9 brd ff:ff:ff:ff:ff:ff
4: gre0: <NOARP,UP> mtu 1476 qdisc noqueue
link/gre 0.0.0.0 brd 0.0.0.0
5: gretun@eth0: <POINTOPOINT,NOARP,UP> mtu 8776 qdisc noqueue
link/gre 66.1.1.161 peer 66.1.2.161
root@den1tun01:/home/root $ ip tun
gre0: gre/ip remote any local any ttl inherit nopmtudisc
gretun: gre/ip remote 66.1.2.161 local 66.1.1.161 dev eth0 ttl 20
root@den1tun01:/home/root $ ifconfig
eth0 Link encap:Ethernet HWaddr 00:19:B9:DD:FF:D9
inet addr:10.1.2.243 Bcast:10.1.3.255 Mask:255.255.254.0
UP BROADCAST RUNNING MULTICAST MTU:8800 Metric:1
RX packets:3357 errors:0 dropped:0 overruns:0 frame:0
TX packets:484 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:230757 (225.3 KiB) TX bytes:63937 (62.4 KiB)
Interrupt:169 Memory:f8000000-f8011100
eth0.2 Link encap:Ethernet HWaddr 00:19:B9:DD:FF:D9
inet addr:66.1.1.161 Bcast:66.1.1.191 Mask:255.255.255.192
UP BROADCAST RUNNING MULTICAST MTU:8800 Metric:1
RX packets:950 errors:0 dropped:0 overruns:0 frame:0
TX packets:20 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:43860 (42.8 KiB) TX bytes:1200 (1.1 KiB)
gretun Link encap:UNSPEC HWaddr
42-0B-33-A1-FF-C0-00-00-00-00-00-00-00-00-00-00
inet addr:10.253.253.1 P-t-P:10.253.253.2 Mask:255.255.255.0
UP POINTOPOINT RUNNING NOARP MTU:8776 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:7 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:756 (756.0 b)
gre0 Link encap:UNSPEC HWaddr
00-00-00-00-FF-00-00-00-00-00-00-00-00-00-00-00
UP RUNNING NOARP MTU:1476 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:225 errors:0 dropped:0 overruns:0 frame:0
TX packets:225 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:13271 (12.9 KiB) TX bytes:13271 (12.9 KiB)
I've also tried changing the destination for the route to the near end of
the private subnet and tried pinging various things on the tunnel subnet and
remote network to create "interesting traffic" to bring the tunnel up but
tcpdump still shows nothing.
Then I noticed that ping does show an error count:
[root@den1tun01 ~]# ping 10.253.253.2
PING 10.253.253.2 (10.253.253.2) 56(84) bytes of data.
>From 10.253.253.1 icmp_seq=0 Destination Host Unreachable
>From 10.253.253.1 icmp_seq=1 Destination Host Unreachable
--- 10.253.253.2 ping statistics ---
2 packets transmitted, 0 received, +2 errors, 100% packet loss, time 1000ms
, pipe 2
I can ping the local end: 10.253.253.1, but the tunnel is still
non-functinoal.
Thanks!
Greg
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