(as far as i know if we don't have full-mesh and synchronization is on, we can see the routes learned from our IBGP peers in the BGP table but all marked with * , so none of them will be added into the routing table).a BGP border router would not propagate a BGP advertisement to an eBGP peer until the router does see the same IP prefix learned in IGP ( OSPF, ISIS or other internal protocol).We are receiving the full-bgp table from our upstreams.In old times not all routers were BGP speakers so the rule was added by Cisco and enabled by default.RQ: our ibgp peers are loopback interfaces advertised via ospf, next-hop-self is configured between them.the BGP synchronization was an old routing loop prevention mechanism that worked in the following way:Please have a look at this two linksPlease clarify and thank you in advance.However when i perform : sh ip bgp sum router bgp 200 no synchronization bgp log-neighbor-changes redistribute ospf 110 neighbor 3.3.3.3 remote-as 200 neighbor 3.3.3.3 update-source Loopback0 neighbor 4.4.4.4 remote-as 200 neighbor 4.4.4.4 update-source Loopback0 neighbor 10.10.10.1 remote-as 100 neighbor 10.10.10.1 password cisco no auto-summary The BGP synchronization rule states that a router will not include in its routing table nor advertise routes learned by IBGP unless that route is directly connected or learned from an IGP. Issue the no synchronization command under router bgp in order to disable synchronization. please help me By default, BGP synchronization is disabled. BGP waits until IGP propagates the route within the AS and then advertises it to external peers. router bgp 100 no synchronization Note: 确保之后输入 clear ip bgp address 清除原先的BGP会话. R3 is announcing its loopback interface and R1 sees the advertisement and even puts it in its routing table. A BGP router with synchronization enabled does not install iBGP learned routes into its routing table if it is not able to validate those routes in its IGP. I want to check the no synchronisation and no auto summary in BGP packets. In which packet should i check for these informations - (Open/update message ?) Beginning with IOS 12.2(8)T, the default BGP behavior is no synchronization. Intermediate routers only taking part in IGP would know how to route traffic with this destination.- all routers in the AS take part in iBGP ( using BGP RR or confederations this is easy to achieve)- in modern MPLS based networks internal routers ( P nodes) do not perform IP routing but MPLS switching so they can be unaware of IP prefixes and can be not part of the iBGP mesh.So it is something that you should not worry about, it is good to know what is, but it is disabled by default.I am running into a weird situation that could might be related to this issue.I have 3 borders each peering with a different upstream provider via ebgp.What is synchronization, and how does it influence BGP routes installed in the IP routing table?The rule is now by default disabled.PLease expain in brief when do we use bgp synchronization and when do we disable this. “no sync” command : Don’t use or advertise a route which is learnt by IBGP until same route is learnt by an internal routing protocol ( like OSPF etc.
A BGP router with synchronization enabled does not install iBGP learned routes into its routing table if it is not able to validate those routes in its IGP.