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

[Liu, Xuan (UMKC-Student)]

I guess it depends on what OS the node has. 

For CentOS 5.5
[root at control-2 ~]# sysctl -a | grep \\.rp_filter
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 0
net.ipv4.conf.eth0.rp_filter = 1

For my nodes running Ubuntu 12.04:
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.eth1.rp_filter = 1
net.ipv4.conf.eth2.rp_filter = 1
net.ipv4.conf.eth3.rp_filter = 1
net.ipv4.conf.eth4.rp_filter = 1
net.ipv4.conf.eth5.rp_filter = 1
net.ipv4.conf.eth6.rp_filter = 1

On ubuntu system, I need to run following command to turn off the reverse path filtering (assuming all my virtual interfaces are ethX, X is not 0) 
sudo sysctl -w net.ipv4.conf.all.rp_filter=0
sudo sysctl -w net.ipv4.conf.default.rp_filter=0
# turn off the reverse path filtering for eth1 ~ eth6
/sbin/ifconfig -a | grep eth | awk '{ if (substr($1, 4,4) != 0) { print "sudo sysctl -w net.ipv4.conf." $1 ".rp_filter=0"}}' | sh

Then it looks like:
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.default.rp_filter = 0
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.eth1.rp_filter = 0
net.ipv4.conf.eth2.rp_filter = 0
net.ipv4.conf.eth3.rp_filter = 0
net.ipv4.conf.eth4.rp_filter = 0
net.ipv4.conf.eth5.rp_filter = 0
net.ipv4.conf.eth6.rp_filter = 0

I only tested XORP on Fedora and Ubuntu, so I'm not sure if this only happens to Ubuntu system. 

So maybe it's better to have a note in the XORP installation instruction, so that the users can be aware of this potential issue. 

Thanks,

-- Xuan





________________________________________
From: Ben Greear <greearb at candelatech.com>
Sent: Tuesday, August 5, 2014 5:18 PM
To: Liu, Xuan (UMKC-Student)
Cc: Avinash Sridharan; xorp-users at xorp.org
Subject: Re: [Xorp-users] FW: cannot ping one of the interfaces from an OSPF router after installing XORP

On 08/05/2014 03:05 PM, Liu, Xuan (UMKC-Student) wrote:
> Okay, I just figured it out. I needs to turn off the reverse path filtering on my VM, by default it's 1.
>
>
> sudo sysctl -w net.ipv4.conf.all.rp_filter=0
>
> sudo sysctl -w net.ipv4.conf.default.rp_filter=0
>
>
> I also did similar thing to all other interfaces (eth1, eth2, ...)
>
>
> Here is a bug report about this issue for ubuntu server 10.04 that has Quagga installed.
>
>
> https://bugs.launchpad.net/ubuntu/+source/quagga/+bug/625812
>
>
> Thank you for all the helps

Is this something that Xorp could detect on startup and warn the user about, perhaps?

If so, a patch (against latest code in git) would be welcome.

Thanks,
Ben

--
Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com