BGP - Network not being advertised.

RouterOS General
1

Hi there,

We are having a problem with advertising a range of public IP’s from our main breakout router which has a BGP session with our Back haul provider. The two networks 188.95.40.0/21 and 46.227.144.0/21 are defined in the /BGP/Networks but only one of them the “188.95..” is being advertised and the other one is not. I have copied the configs below. Could you please advise.

Thanks.


/routing bgp instance> print
Flags: X - disabled
0 name=“default” as=49441 router-id=0.0.0.0 redistribute-connected=yes redistribute-static=yes redistribute-rip=yes redistribute-ospf=no
redistribute-other-bgp=no out-filter=“” client-to-client-reflection=yes ignore-as-path-len=no routing-table=“”


/routing bgp network> print
Flags: X - disabled

NETWORK SYNCHRONIZE

0 188.95.40.0/21 yes
1 46.227.144.0/21 yes


/routing bgp advertisements> print
PEER PREFIX NEXTHOP AS-PATH ORIGIN LOCAL-PREF
Goscomb 188.95.40.0/23 93.89.94.174 igp
Goscomb 188.95.40.0/21 93.89.94.174 igp
Gradw… 188.95.40.0/23 79.135.121.6 igp
Gradw… 188.95.40.0/21 79.135.121.6


/routing bgp peer> print
Flags: X - disabled, E - established

INSTANCE REMOTE-ADDRESS REMOTE-AS

0 E default 93.89.94.173 39326
1 E default 79.135.121.5 29676


/routing bgp> export

feb/03/2012 09:53:30 by RouterOS 4.15

software id = MXT6-VSKC

/routing bgp instance
set default as=49441 client-to-client-reflection=yes comment=“” disabled=no ignore-as-path-len=no name=default out-filter=“” redistribute-connected=
yes redistribute-ospf=no redistribute-other-bgp=no redistribute-rip=yes redistribute-static=yes router-id=0.0.0.0 routing-table=“”
/routing bgp network
add comment=“” disabled=no network=188.95.40.0/21 synchronize=yes
add comment=“” disabled=no network=46.227.144.0/21 synchronize=yes
/routing bgp peer
add address-families=ip as-override=no comment=“” default-originate=never disabled=no hold-time=3m in-filter=bgp-in instance=default multihop=no
name=Goscomb nexthop-choice=default out-filter=bgp-out passive=no remote-address=93.89.94.173 remote-as=39326 remove-private-as=yes
route-reflect=no tcp-md5-key=“” ttl=default use-bfd=no
add address-families=ip as-override=no comment=“” default-originate=never disabled=no hold-time=3m in-filter=bgp-in instance=default multihop=no
name=Gradwell1 nexthop-choice=force-self out-filter=bgp-out passive=no remote-address=79.135.121.5 remote-as=29676 remove-private-as=no
route-reflect=no tcp-md5-key=“” ttl=default use-bfd=no
add address-families=ip as-override=no comment=“” default-originate=never disabled=yes hold-time=3m in-filter=bgp-in instance=default multihop=yes
name=Hambo nexthop-choice=default out-filter=bgp-out passive=no remote-address=188.95.44.66 remote-as=56329 remove-private-as=no route-reflect=no
tcp-md5-key=“” ttl=default use-bfd=no

2

If you don’t have exact route in routing table then turn off synchronization

3

Thanks lot for this mrz, that actually solved the problem. So whats the basic purpose of the synchronize feature?

4

Synchronize allows you to only advertise a route when your iBGP or OSPF actually knows how to route it. There are a number of scenarios in which this makes sense.

Most recently I used this when building some failover routes. Two routers connect to an upstream and have different paths (multiple routing hops) to the client subnet. If one of the paths breaks i don’t want that specific border router to announce the subnet any more. Using sync this becomes automatic.

Regardt

5

Thats great. Thanks regardtv.