BGP problem

[simon.hart]

Hi am getting quite lost and am desperate need of some help.

I am try to set up a fairly simple BGP session between a 2500 and 3550. I am trying to advertise loopback addresses between each device, but with very little success.

The 2500 is in AS 254 and the 3550 is in AS 200. The loopbacks that I am trying to advertise are 10.10.10.1 on the 2500 and 20.20.20.1 on the 3550. However neither networks appear within the BGP table of either the router or the switch.

Configurations below

2500 Config

router bgp 254

bgp log-neighbor-changes

network 10.10.10.1 mask 255.255.255.0

neighbor 192.10.1.8 remote-as 200

!

router bgp 254

bgp log-neighbor-changes

network 10.10.10.1 mask 255.255.255.0

neighbor 192.10.1.8 remote-as 200

2500 show ip route output

10.0.0.0/24 is subnetted, 1 subnets

C 10.10.10.0 is directly connected, Loopback1

C 192.10.1.0/24 is directly connected, Ethernet0

2500 show ip bgp sum

BGP router identifier 10.10.10.1, local AS number 254

BGP table version is 7, main routing table version 7

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

192.10.1.8 4 200 59 58 7 0 0 00:06:31 0

__________________________________________________________________

3550 config

interface Loopback1

ip address 20.20.20.1 255.255.255.0

!

router bgp 200

bgp log-neighbor-changes

network 20.20.20.1 mask 255.255.255.0

neighbor 192.10.1.254 remote-as 254

3550 sh ip route

20.0.0.0/24 is subnetted, 1 subnets

C 20.20.20.0 is directly connected, Loopback1

183.0.0.0/24 is subnetted, 2 subnets

C 183.0.58.0 is directly connected, FastEthernet0/15

C 183.0.17.0 is directly connected, FastEthernet0/1

C 192.10.1.0/24 is directly connected, Vlan82

3550 sh ip bgp sum

BGP router identifier 20.20.20.1, local AS number 200

BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd

192.10.1.254 4 254 61 62 1 0 0 00:09:10 0

__________________________________________________________________

The 'show ip bgp' command on both the router and switch are blank, even after a clear ip bgp *.

If I use the redistribute connected command, then the networks appear in the bgp table and are exchanged between the two networks. However the routes that are advertised are classful.

I really want to advertise these networks using the Network X.X.X.X mask X.X.X.X command.

Any help on this will be very much appreciated

Simon

[Georg Pauwen]

Hello Simon,

two things about your configuration:

Both your BGP routers have synchronization enabled, which means that they will not advertise a network unless it is learned through an IGP. That is why you do see the networks being advertised when you redistribute the routes as connected.

Also, you have auto-summary enabled, which causes the networks to be advertised as classfull.

Change your configurations as following:

2500

router bgp 254

--> no synchronization

bgp log-neighbor-changes

network 10.10.10.1 mask 255.255.255.0

neighbor 192.10.1.8 remote-as 200

--> no auto-summary

3550

router bgp 200

--> no synchronization

bgp log-neighbor-changes

network 20.20.20.1 mask 255.255.255.0

neighbor 192.10.1.254 remote-as 254

--> no auto-summary

Regards,

GP

[simon.hart]

Hi thanks for your reply, however this I do not believe this is the problem.

The problem I am having is that the bgp table is not getting populated.

As I understand it, the bgp table will be populated with prefixes. If you have synchronisation enabled the prefixes will not be loaded into the Route Table (RIB) unless it knows how to get to the network via an underlying IGP.

The auto-summary I thought may have been the issue, however I have turned this on and off to see what happens, again nothing is being populated in the bgp table (sh ip bgp = zilch!!).

Having said all that I have tried your suggestions but still to no avail!!

Thanks

Simon

[Kevin Dorrell]

I don't know very much about BGP, but don't you need network 10.10.10.0 mask 255.255.255.0 on the 2500, and network 20.20.20.0 mask 255.255.255.0 on the 3550? That is, the subnet base addresses rather than the host address? But like I say, I don't know BGP very well yet.

Kevin Dorrell

Luxembourg

[Harold Ritter]

Kevin,

You are absolutely right. Correcting the network statement will fix the issue.

[simon.hart]

Hi Keving and Hritter,

You know I am pretty certain you are both right here. Although I have not tested it, I now know that is what the problem is.

Sometimes you get to a point were you really cannot see the wood for the trees!!

Thanks for your responses

Simon

[Georg Pauwen]

Harold,

is this IOS version dependent ? I labbed the exact config of Simon and with my routers, the routes got advertised just fine, it looks like the network statement looks at the mask and then advertises just 10.10.10.0 and 20.20.20.0.

Regards,

Georg

[Kevin Dorrell]

That's very odd. I cannot find anything about it being version dependent, but this is what I get with 12.2(17a):

router bgp 200

bgp log-neighbor-changes

network 20.20.20.1 mask 255.255.255.0

!

Okeeffe#show ip bgp

Okeeffe#

Okeeffe#conf t

Enter configuration commands, one per line. End with CNTL/Z.

Okeeffe(config)#router bgp 200

Okeeffe(config-router)#no network 20.20.20.1 mask 255.255.255.0

Okeeffe(config-router)#network 20.20.20.0 mask 255.255.255.0

Okeeffe(config-router)#^Z

Okeeffe#

02:24:01: %SYS-5-CONFIG_I: Configured from console by console

Okeeffe#show ip bgp

BGP table version is 2, local router ID is 20.20.20.1

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

*> 20.20.20.0/24 0.0.0.0 0 32768 i

OK, I only had time to test it locally on one router. (I shouldn't be so lazy, but I didn't want to interfere with another experiment I am running at the moment ;-) But it does seem to suggest the route will not be advertised unless it matches the routing table entry exactly.

I would be interested to see how this issue resolves.

Kevin Dorrell

Luxembourg

[Georg Pauwen]

Kevin, Harold, Simon,

my mistake, I left the ´redistributed connected´ in my config inadvertently...

The exact match is indeed required...

Thanks for the clarification !

Regards,

Georg

[tanveer210]

Dear all

see the following configuration for the BGP peering

As two AS number are different so EBGP peer will be created see the configuration below

ROUTER 2500

ip loopback 0

ip address 10.10.10.1 255.255.255.255

interface serial0

ip address 1.1.1.1 255.255.255.0

router bgp 254

neighbor 20.20.20.1 remote-as 200

neighbor 20.20.20.1 ebgp-multihop 2

neighbor 20.20.20.1 update-source Loopback0

ip route 20.20.20.1 255.255.255.255 1.1.1.2

Router 3500

ip loopback 0

ip address 20.20.20.1 255.255.255.255

interface serial0

ip address 1.1.1.2 255.255.255.0

router bgp 200

neighbor 10.10.10.1 remote-as 200

neighbor 10.10.10.1 ebgp-multihop 2

neighbor 10.10.10.1 update-source Loopback0

ip route 10.10.10.1 255.255.255.255 1.1.1.1

after doing these configuration check with the following commands

show ip bgp neighbors | include BGP

BGP state = Established,

and check with show ip bgp summary

hope it would be helpful for you

Regards