[CentOS] Ipv6 addr with Vlan-Id - unable to ping neighbour

Rohit Mediratta rohit_medi at hotmail.com
Thu Nov 18 01:37:22 EST 2010


Hi All,
   If I have a vlan-Id on an interface with an ipv6 address, then I am unable to ping a real router.
The problem is that the Neighbour Solicitation originated from the Centos machine is missing the Vlan-Id in the packet.
Therefore a real router will drop such a packet.
I have tried this with Centos 4.7 and with Centos 5.5 with the same result.



If I originate the first Neighbour Solicitation from the Router (which contains the Vlan-Id), then Linux learns the Mac address correctly and bidirectional ping works.
This is a workaround that I am using at the moment, but I would like to avoid doing this all the time (especially when there is a timeout of the neighbour information).


This problem does not exist for Ipv4 (i.e. ARP packets originated from Centos contain the Vlan-Id as expected).


Here is my topology.
Router--port1/1/1.1-------------------eth2---(eth2.1)--Centos
          10.10.8.1/24                     1.1.1.2   10.10.8.10
       (3ffe::a0a:801/120)                           (3ffe::a0a:80a/120)
           port 1/1/1.21--------------------------eth2.21
       (3ffe::a0f:801/120)                            (3ffe::a0f:80a/120)
          

(KANRTB1):~ > cat /etc/*-release
CentOS release 5.5 (Final)
(KANRTB1):~ > cat /proc/version
Linux version 2.6.18-194.el5 (mockbuild at builder16.centos.org) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-48)) #1 SMP Fri Apr 2 14:58:35 EDT 2010


(KANRTB1):~ > ip -6 addr show
<SNIP>
687: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 500
    inet6 3ffe::a0f:80a/128 scope global
       valid_lft forever preferred_lft forever
    inet6 3ffe::a0a:80a/120 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::2ff:7ff:fe00:2/64 scope link
       valid_lft forever preferred_lft forever
<SNIP>
692: eth2.1 at eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500
    inet6 3ffe::a0a:80a/120 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::2ff:7ff:fe00:2/64 scope link
       valid_lft forever preferred_lft forever
693: eth2.21 at eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500
    inet6 3ffe::a0f:80a/120 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::2ff:7ff:fe00:2/64 scope link
       valid_lft forever preferred_lft forever
<SNIP>


KANRTB1):~ > ifconfig
<SNIP>

eth2      Link encap:Ethernet  HWaddr 00:FF:07:00:00:02
          inet addr:1.1.1.2  Bcast:1.1.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:29 errors:0 dropped:0 overruns:0 frame:0
          TX packets:313 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500
          RX bytes:3330 (3.2 KiB)  TX bytes:48442 (47.3 KiB)

eth2.1    Link encap:Ethernet  HWaddr 00:FF:07:00:00:02
          inet addr:10.10.8.10  Bcast:10.10.8.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:29 errors:0 dropped:0 overruns:0 frame:0
          TX packets:64 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:2924 (2.8 KiB)  TX bytes:10071 (9.8 KiB)


eth2.21   Link encap:Ethernet  HWaddr 00:FF:07:00:00:02
          inet addr:10.15.8.10  Bcast:10.15.8.10  Mask:255.255.255.255
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:34 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:6313 (6.1 KiB)

<SNIP>

Any help/easy fixes/pointers are much appreciated.
thanks,
Rohit

 		 	   		  
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