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<div class="moz-cite-prefix">Hello,
<br>
<br>
I think our scenario does not contradicts with BGP standard (RFC
4271 5.1.3).
<br>
<br>
Assuming a Bird RS with 2 interfaces:
<br>
-------------------------------------------------------------------------------------------<br>
192.168.0.1/24 eth0 <--> <b>BIRD</b><b> RS</b><-->
eth1 10.0.0.1/24
<br>
-------------------------------------------------------------------------------------------<br>
<br>
We would like to manually set hext hop(192.168.0.50) of certain
routes advertised to BGP neighbors in the segment 192.168.0.0/24.
<br>
(There is no case that a next hop of 192.168.0.50 would be
advertised to a peer in 10.0.0.0/24)
<br>
<br>
Having a setup with a single Bird interface everything works fine:<br>
-------------------------------------------------------------------------------------------<br>
<b>BIRD RS</b> <--> eth0 192.168.0.1/24 | eth0 alias
10.0.0.1/24
<br>
-------------------------------------------------------------------------------------------<br>
<br>
Best~<br>
<br>
On 01/24/2013 10:27 PM, Ondrej Zajicek wrote:<br>
</div>
<blockquote cite="mid:20130124202737.GC22191@localhost" type="cite">
<pre wrap="">On Wed, Jan 23, 2013 at 01:33:16PM +0200, Javor Kliachev wrote:
</pre>
<blockquote type="cite">
<pre wrap=""> Hello,
We're using BIRD on Linux Debian 6 as a BGP route server with two subnets.
We would also like to manually change the next hop of certain prefixes and
peers.
When both subnets are configured at the single physical interface or in
alias
mode everything works fine. As soon as we configure any of the subnet at a
vlan
interface the next hop manipulation fails and the ip address of the RS is
set instead.
Any ideas what is the reason for this behaviour?
</pre>
</blockquote>
<pre wrap="">
Hello
The reason is BGP standard (RFC 4271 5.1.3). The next hop modification
in the export filter is processed and after that standard BGP processing
of next hop is done, which, in this case, replace the next hop with
local address because conditions that would allow to send supplied one
are not met (which is essentially matching iface based on subnet check
for single-hop eBGP).
</pre>
</blockquote>
<br>
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---<br>
<strong>Javor Kliachev</strong><br>
IP engineer<br>
<br>
Neterra Ltd.<br>
Telephone: +359 2 975 16 16<br>
Fax: +359 2 975 34 36<br>
Mobile: +359 885 988 495 <br>
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<a href="http://www.neterra.net" class="txt2">www.neterra.net</a>
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