SV: BGP with wrong netmask on wan interface

[Magnus Löfqvist]

Hi,

Yes, you are correct.
But we have routes for 10.9.140.0/22 (OpenVPN transport network)

ip ro sh:
default via 10.6.52.59 dev wwan0
10.0.0.0/8 dev wwan0  proto kernel  scope link  src 10.6.52.58
10.9.140.0/22 dev tap0  proto kernel  scope link  src 10.9.140.33

Bird:
bird> show route
0.0.0.0/0          via 10.6.52.59 on wwan0 [kernel1 09:43:55] * (10)
10.9.140.0/22      dev tap0 [direct1 09:44:12] * (240)

So why are not BGP traffic to 10.9.140.1 going thru tap0 ?




Med vänlig hälsning / Best regards
Magnus Löfqvist

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Från: green at highloadlab.com [mailto:green at highloadlab.com] För Alexander Zubkov
Skickat: den 8 november 2017 10:16
Till: Magnus Löfqvist <ml at vmi.se>
Kopia: bird-users at network.cz
Ämne: Re: BGP with wrong netmask on wan interface

Hi,
You have:
WAN (Mobile): 10.6.90.187 / 255.0.0.0
OpenVPN interface (tap0):  10.9.140.33 / 255.255.252.0

protocol bgp BGP1 from RR_LTE { neighbor 10.9.140.1 as 1; preference 140;};

So you are trying to reach 10.9.140.1. If you have no additional routes, than this address falls into
10.6.90.187 / 255.0.0.0 network, i.e. WAN interface and will be routed there.

On Wed, Nov 8, 2017 at 8:20 AM, Magnus Löfqvist <ml at vmi.se<mailto:ml at vmi.se>> wrote:
Hi,

I have some mobile routers (connected over LTE) and with openvpn.

Over the openvpn we are running a BGP to allow distribute some routes and export routes.

Some of the routers are having wrong netmask (255.0.0.0 instead of 255.255.255.252).
This seems to work (ie internet are working, and the openvpn connection is established).

But when we are trying to get the BGP connection up, it tries to send the BGP connection over the WAN istead of openvpn connection.
I guess that I have made some mistake in the config.
It should take smaller path before matching the larger..


WAN (Mobile): 10.6.90.187 / 255.0.0.0
OpenVPN interface (tap0):  10.9.140.33 / 255.255.252.0

Bird config:

template bgp RR_LTE {
        debug all;                                  # debug BGP
        description "BIRD RR";
        local as 1;                                 # the AS used by the local BGP speaker
        direct;
        gateway direct;
        import filter import_ATM;                                 # just accept everything
        export filter export_ATM;                                 # and advertise it to all the neigbors
        connect retry time 10;                      # reconnect try after 10s
        hold time 240;                               # hold time send in BGP messages
}

protocol bgp BGP1 from RR_LTE { neighbor 10.9.140.1 as 1; preference 140;};

root at client1:/etc# tcpdump -ni wwan0 tcp port 179 and host 10.9.140.1
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on wwan0, link-type EN10MB (Ethernet), capture size 65535 bytes
15:29:08.755188 IP 10.6.90.187.34974 > 10.9.140.1.179: Flags [S], seq 1482209106, win 14600, options [mss 1460,sackOK,TS val 88007 ecr 0,nop,wscale 8], length 0
15:29:11.762726 IP 10.6.90.187.45591 > 10.9.140.1.179: Flags [S], seq 1681977930, win 14600, options [mss 1460,sackOK,TS val 88307 ecr 0,nop,wscale 8], length 0



Med vänlig hälsning / Best regards
Magnus Löfqvist


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