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I'm doing some labs with Quagga on Ubuntu 10.04 LTS as a BGP router in a multihomed and multi router setup. Currently I have setup a fake "ISP" router in my lab and have my two Quagga routers behind it sharing routes with iBGP and I have ran into some issues that I can't seem to find a answer to.

My network setup looks like this .

R1 and R2 is connected with a link network ( and are both connected to the same shared subnet of The link network and shared subnet are on different VLANs.

R1 and R2 will be connected to one ISP each and will announce to their ISP peers. It will be internaly subneted but to avoid beeing filtered a larger subnet will be announced.

The routers will have a floating IP that they share between themselfs (if one router goes down the other should take over) using uCARP.

Now to my problem. If I issue traceroute or ping from ISP1 to ip everything goes smoothly and I get reply. If I do the same to ip I get Request timeout.

I see the ICMP echo request on the router that have assing to it's interface but it's like it don't know where to send the reply.

I have tried to Google for an answer but have come up empty handed. Tried a few solutions but nothing seems to work.

Is there any fault in my network design? I know that if I use the same subnet as shared subnet and linknet everything works fine except that machines behind the routers get a ICMP Redirect message when using ping and I think that is not a good implementation.

What I think happens is that the traffic destined for is directed thru VLAN15 interface on R1 and when R2 (that has assigned to it) it don't uses routing to get to ISP1 ip that are sending the ICMP Echo Request.

I can reach every network from each router (for example I can reach ISP1 interface) but not if I use as source on R2. On R1 I can use as source without any trouble.

IP Plan for routers.


  • eth0 =
  • eth1 =


  • eth0 =
  • eth1.10 = (This is a VLAN interface for segmentation of LAN)
  • eth1.15 = (Also VLAN interface)


  • eth1.10 = (VLAN Interface)
  • eth1.15 = (VLAN interface)

My Quagga BGPd conf looks like this: ISP1 router bgp 65414 bgp router-id network network neighbor remote-as 65515 neighbor description R1

R1 router bgp 64515 bgp router-id network neighbor remote-as 65515 neighbor description R2 neighbor next-hop-self neighbor remote-as 65514 neighbor description ISP1 neighbor prefix-list isp1_filter_out out

ip prefix-list isp1_filter_out seq 5 permit ip prefix-list isp1_filter_out seq 999 deny ge 1

R2 router bgp 65515 bgp router-id network neighbor remote-as 65515 neighbor description R2 neighbor next-hop-self

Any thought? Is the issue in Linux or Quagga? Do you need anything more from me regarding my setup?

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What is the 'floating ip' mechanism? Is this HSRP-like using as the shared virtual IP, and 1.1 on R1 and 1.2 on R2? I also don't understand where VLAN15 on R1 came in. Please edit the question so that each router's interfaces, ports, and subnets are listed in a simple (tabular) format. – Aaron Dec 8 '11 at 18:56
Will be using uCARP for floating IP. Also I have updated the original question with your requests. – Andreas Falck Dec 9 '11 at 7:46
up vote 0 down vote accepted

Just wanted to inform that I got some help from the Quagga-users mailing list in solving this and that this issue is resolved now.

For future reference I think that it's a good idea that I post the solution if anyone else encounters the same issue as I did.

The issue was with Ubuntu having net.ipv4.conf.all.rp_filter and net.ipv4.conf.default.rp_filter set to enabled by default. This was preventing packets from entering on one interface and leaving on another.

The suggestion in Ubuntu Bugs report (see link below) is that rp_filter is disabled when installed Quagga but this is not yet implemented.

Quagga-users mailinglist thread
Ubuntu Bugs report

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