BGP with wrong netmask on wan interface

[Alexander Zubkov]

In that case it probably because you are using direct (not multihop) bgp
session and bird binds to the interface which have this address in its
direct network - wwan0. In that case only routes with dev wwan0 will be
applied. I think you want to use multihop bgp session. If you want to use
direct session and this address is accepted directly via tap0, than I think
specifying source address from tap0 in bgp session should work.

On Wed, Nov 8, 2017 at 10:47 AM, Magnus Löfqvist <ml at vmi.se> wrote:

> 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> 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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