[Xorp-users] FW: cannot ping one of the interfaces from an OSPF router after installing XORP

Tue Aug 5 10:45:09 PDT 2014

May be the arp-cache timeout is too low? You can check the timeout
value /proc/sys/net/ipv4/neigh/eth0/gc_stale_time
here. If its too low see if changing it to larger value helps.

On Tue, Aug 5, 2014 at 10:28 AM, Liu, Xuan (UMKC-Student) <
xuan.liu at mail.umkc.edu> wrote:

>  
>
> Thank you Avinash, apparently, I can ping rt-5: eth5 and eth3 now, without
> doing anything. But now I cannot ping rt-4:eth2 (192.168.2.2) from rt-2.
> rt-4:eth2 has received the ping request from rt-2.
>
>
>  From the routing table at rt-4:
>
>
>  xuanliu at rt-4:~$ ip route show
> default via 172.16.0.1 dev eth0
> 172.16.0.0/12 dev eth0  proto kernel  scope link  src 172.17.2.8
> 192.168.1.0/24 via 192.168.2.1 dev eth2  proto xorp  metric 20 notify
> 192.168.2.0/24 dev eth2  proto kernel  scope link  src 192.168.2.2
> 192.168.3.0/24 via 192.168.13.2 dev eth3  proto xorp  metric 20 notify
> 192.168.6.0/24 via 192.168.2.1 dev eth2  proto xorp  metric 30 notify
> 192.168.7.0/24 via 192.168.13.2 dev eth3  proto xorp  metric 20 notify
> 192.168.10.0/24 via 192.168.13.2 dev eth3  proto xorp  metric 20 notify
> 192.168.13.0/24 dev eth3  proto kernel  scope link  src 192.168.13.1
>
>
>  The ARP cache on rt-4 shows
>  xuanliu at rt-4:~$ arp -n
> Address                  HWtype  HWaddress           Flags Mask
>  Iface
> 172.16.0.3               ether   fe:ff:ff:ff:ff:ff   C
> eth0
> 192.168.2.1              ether   02:18:08:46:10:53   C
> eth2
> 172.16.0.1               ether   fe:ff:ff:ff:ff:ff   C
> eth0
>
>
> There is no resolution for 192.168.13.2, which is the return path for the
> ping reply, according to the routing table.
>
> However, the ARP cache keeps changing, and now it shows the all the
> interfaces, and the ping works.
>
>  xuanliu at rt-4:~$ arp -n
> Address                  HWtype  HWaddress           Flags Mask
>  Iface
> 192.168.13.2             ether   02:41:88:70:16:d2   C
> eth3
> 192.168.2.1              ether   02:18:08:46:10:53   C
> eth2
> 172.16.0.1               ether   fe:ff:ff:ff:ff:ff   C
> eth0
>
>
>  Thanks,
>
>  -- Xuan
>
>
>    ------------------------------
> *From:* Avinash Sridharan <avinash.sridharan at gmail.com>
> *Sent:* Tuesday, August 5, 2014 11:01 AM
> *To:* Liu, Xuan (UMKC-Student)
> *Cc:* xorp-users at xorp.org
> *Subject:* Re: [Xorp-users] cannot ping one of the interfaces from an
> OSPF router after installing XORP
>
>  Look at whats being programmed in the kernel route tables in router 5.
> Something like "ip route show" command should give you the routing table
> programmed in the linux kernel. It might give you some idea as to why the
> ICMP response is not being sent out. Also, make sure the ARP cache on
> router 5 has the ARPs resolve for 192.168.13.1 on router 5.
>
>
> On Tue, Aug 5, 2014 at 8:32 AM, Liu, Xuan (UMKC-Student) <
> xuan.liu at mail.umkc.edu> wrote:
>
>>  Hello,
>>
>>
>>  I have came across this problem when I have configured a simple
>> five-node network running OSPF protocol. The topology looks like
>>
>>
>>                    1 --------------- 2
>>
>>                 /  \                   / \
>>
>>               /      \               /    |
>>
>>               4       \           /       3
>>
>>               |         \        /        |
>>
>>                \          \     /        /
>>
>>                  \         \  /        /
>>
>>                    \------ 5 -----/
>>
>>
>>  The link information is : rt1:eth4 -- rt2:eth1: 192.168.1.1 -
>> 192.168.1.2
>>
>>                                         rt2:eth4 -- rt3:eth3: 192.168.6.1
>> - 192.168.6.2
>>
>>                                         rt3:eth2 -- rt5:eth2: 192.168.10.1
>> - 192.168.10.2
>>
>>                                         rt5:eth1 -- rt4:eth3: 192.168.13.2 -
>> 192.168.13.1
>>
>>                                         rt4:eth2 -- rt1:eth2: 192.168.2.2
>> - 192.168.2.1
>>
>>                                         rt1:eth3 -- rt5:eth3: 192.168.3.1
>> - 192.168.3.2
>>
>>                                         rt2:eth2 -- rt5:eth5: 192.168.7.1
>> - 192.168.7.2
>>
>> All link has prefix 24.
>>
>>
>>  Each node runs Ubuntu 12.04 OS, and I have installed XORP 1.8.5. For
>> each node, I have configured it as an OSPF router. Most of the routing
>> looks fine to me, except for some interfaces. For example:
>>
>>
>>  If I send ping request from rt1 to 192.168.7.2 (rt5), I got no
>> response. The routing table at rt1, rt5 are like:
>>
>>
>>  root at rt-1> show route table ipv4 unicast ospf
>> 192.168.6.0/24 [ospf(110)/20]
>> > to 192.168.1.2 via eth4/eth4
>> 192.168.7.0/24 [ospf(110)/20]
>> > to 192.168.1.2 via eth4/eth4
>> 192.168.10.0/24 [ospf(110)/20]
>> > to 192.168.3.2 via eth3/eth3
>> 192.168.13.0/24 [ospf(110)/20]
>> > to 192.168.2.2 via eth2/eth2
>>
>>
>>
>>  root at rt-5> show route table ipv4 unicast ospf
>> 192.168.1.0/24 [ospf(110)/20]
>> > to 192.168.3.1 via eth3/eth3
>> 192.168.2.0/24 [ospf(110)/20]
>> > to 192.168.3.1 via eth3/eth3
>> 192.168.6.0/24 [ospf(110)/20]
>> > to 192.168.10.1 via eth2/eth2
>>
>>
>>  I ran tcpdump at rt1, rt2 and rt5 and found that
>>
>>
>>  At rt-2 eth1:
>>  xuanliu at rt-2:~$ sudo tcpdump -i eth1 icmp -n
>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>> listening on eth1, link-type EN10MB (Ethernet), capture size 65535 bytes
>> 11:22:58.797404 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 265, length 64
>> 11:22:59.805624 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 266, length 64
>> 11:23:00.813283 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 267, length 64
>> 11:23:01.821354 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 268, length 64
>>
>>
>>  At rt-2 eth2:
>>  xuanliu at rt-2:~$ sudo tcpdump -i eth2 icmp -n
>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>> listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
>> 11:24:08.347513 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 334, length 64
>> 11:24:09.355769 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 335, length 64
>> 11:24:10.363503 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 336, length 64
>>
>>  At rt-5 eth5:
>>  xuanliu at rt-5:/usr/local/xorp/sbin$ sudo tcpdump -i eth5 icmp -n
>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>> listening on eth5, link-type EN10MB (Ethernet), capture size 65535 bytes
>> 11:24:52.122424 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 376, length 64
>> 11:24:53.130022 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 377, length 64
>> 11:24:54.138424 IP 192.168.1.1 > 192.168.7.2: ICMP echo request, id
>> 11873, seq 378, length 64
>>
>>  Based on the routing table at rt-5, the packet to 192.168.1.0 should be
>> forwarded to link 192.168.3.0. So I checked the interface rt-5:eth3, and it
>> showed nothing.
>>
>>  xuanliu at rt-5:/usr/local/xorp/sbin$ sudo tcpdump -i eth3 icmp -n
>> tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
>> listening on eth3, link-type EN10MB (Ethernet), capture size 65535 bytes
>>
>>
>>  Similarly, I couldn't ping rt-5:eth1 (192.168.13.2) from rt-1 neither.
>> But I can ping 192.168.10.2, and 192.168.10.1, and the packets were
>> forwarded from rt-5:eth3(192.168.3.2) to rt-5:eth2(192.168.10.2)
>>
>>
>>  Could you please provide any suggestion on how to troubleshooting this
>> problem?
>>
>>
>>  Thanks,
>>
>>  -- Xuan Liu
>>
>> _______________________________________________
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>> Xorp-users at xorp.org
>> http://mailman.ICSI.Berkeley.EDU/mailman/listinfo/xorp-users
>>
>>
>
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