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New Member

BGP routes

Why would networks that show up in the BGP table (sh ip bgp) not to get placed in the routing table? For example:

Network Next Hop Metric LocPrf Weight Path

* i10.1.0.0/16 192.168.100.2 100 0 i

* i10.1.1.0/24 192.168.200.1 0 100 0 12345 ?

* i10.1.2.0/24 192.168.200.1 74 100 0 12345 ?

*>i10.1.6.0/24 192.168.100.2 0 100 0 i

* i172.16.30.0/24 192.168.200.1 100 0 12345 i

*>i192.168.100.0 192.168.100.2 0 100 0 i

*>i192.168.200.0 192.168.200.1 0 1000 0 12345 ?

sh ip ro

1.0.0.0/24 is subnetted, 1 subnets

C 1.1.1.0 is directly connected, Loopback111

R 192.168.200.0/24 [120/1] via 192.168.100.2, 00:00:11, Serial0

10.0.0.0/24 is subnetted, 1 subnets

R 10.1.6.0 [120/1] via 192.168.100.2, 00:00:11, Serial0

C 192.168.1.0/24 is directly connected, Ethernet0

C 192.168.100.0/24 is directly connected, Serial0

S* 0.0.0.0/0 [1/0] via 192.168.1.1

Any ideas?

Regards to all,

Joe

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

Re: BGP routes

The BGP next hop is reachable, so it has to be a syncronization issue. Add "no synchronization" under the BGP process. It should take care of it.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
12 REPLIES
New Member

Re: BGP routes

Could you post your BGP configs

Cisco Employee

Re: BGP routes

The BGP next hop is reachable, so it has to be a syncronization issue. Add "no synchronization" under the BGP process. It should take care of it.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: BGP routes

BTW: The best way to determine why the route in the BGP table is not installed in the global routing table is to do a "sh ip bgp x.x.x.x", where x.x.x.x is the prefix you're experiencing issues with. In your case you will see the prefix showing as "not synchronized".

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: BGP routes

Thanks to everyone for the prompt responses.

I'm not in front of my rack at the moment, so this will be a more general note.

"no sync" is configured on the router, but I was under the impression that syncronization was only for advertising networks. BGP would not advertise if the network in question is not already in the routing table. I am not actually advertising any networks under BGP on this router. The routes not appearing in the routing table are being received via it's iBGP peer, which also is receiving routes via eBGP.

More when I have access to the rack.

Once again thanks for the help.

Joe

Gold

Re: BGP routes

"BGP would not advertise if the network in question is not already in the routing table."

Note it doesn't have to be in the routing table from BGP, though.

"I am not actually advertising any networks under BGP on this router."

I assume this means you aren't advertising any routes to your eBGP peers. If this is true, you don't really need "no synchronization" anyway. It shouldn't make any difference either way.

It's kindof odd, though, that you are learning 192.168.100.0 from the neighbor you're peering with over that interface, and through RIP as well. It looks to me like the iBGP peer has a network statement for 192.168.100.0 (?). I would try taking that out, and see if that fixes it, since all of your other routes depend on that one, untimately.

:-)

Russ.W

Cisco Employee

Re: BGP routes

When synchronization is on, BGP waits until the same prefix is installed in the routing table via an IGP before declaring a prefix received iBGP as valid.

The best way for us to help is to have a "sh ip bgp 10.1.1.0" for instance.

This should tell us exactly what the issue is about.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: BGP routes

TermServ#sh ip bgp 172.16.30.0

BGP routing table entry for 172.16.30.0/24, version 0

Paths: (1 available, no best path)

Not advertised to any peer

12345, (aggregated by 12345 192.168.200.1)

192.168.200.1 (metric 1) from 192.168.100.2 (192.168.200.2)

Origin IGP, localpref 100, valid, internal, not synchronized, atomic-aggregate

I feel pretty stupid actually. I just check the router, and "no sync" was not configured. Now it works as it should.

TermServ#sh ip bgp

BGP table version is 8, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete

Network Next Hop Metric LocPrf Weight Path

*>i10.1.0.0/16 192.168.100.2 100 0 i

*>i10.1.1.0/24 192.168.200.1 0 100 0 12345 ?

*>i10.1.2.0/24 192.168.200.1 74 100 0 12345 ?

*>i10.1.6.0/24 192.168.100.2 0 100 0 i

*>i172.16.30.0/24 192.168.200.1 100 0 12345 i

*>i192.168.100.0 192.168.100.2 0 100 0 i

*>i192.168.200.0 192.168.200.1 0 100 0 12345 ?

Going back to what was last posted about syncronisation. So syncronisation does not only apply to advertised (ing) networks? But then this would mean that I would always have to redistribute BGP into an IGP in order to fulfill the syncronisation requirement, and get BGP routes to show in the ip table?

Cisco Employee

Re: BGP routes

That's correct. This is why most people turn synchronization off. I believe in most recent IOS synchronization is turned off by default. It is certainly the case for the 12.0(S) train.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: BGP routes

Just as a precision, synchronization is still usefull in certain scenarios where two iBGP peers exchanges prefixes thru a network that doesn't run BGP. They then have to rely oon the IGP to carry thr transit traffic, hence the need for synchronization. This is seldom seen in service provider networks but kind of usual in entrepise networks using BGP to segment their corporate networks.

Hope this helps,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Gold

Re: BGP routes

It's turned off by default for IPv4 VPNs in 12.2(8)S (CSCdx08292). I was looking for the defect that turned it off for nonVPN peers, but I can't seem to chase that one down.

:-)

Russ.W

Cisco Employee

Re: BGP routes

CSCdz63815 nvgens the "no sync" as soon as you configure BGP.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: BGP routes

Correction, it is CSCdx08881.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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