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Syntax Description:

• neighbor-ip-address— BGP neighbor’s IP address.

• access-list-number— IP access list number.

Purpose: To debug BGP updates from a particular neighbor. The first form debugs all updates from the neighbor. The second form can be used to debug specific updates from the neighbor. The IP access list number can be in the range 1 to 199 or 1300 to 2699.

Cisco IOS Software Release: 10.0

Example 1: Debug All Updates to and from a Particular Neighbor

In Figure 16-2, Router A is advertising four prefixes to Router B, and Router B is advertising four prefixes to Router A. Debug all the updates received from and sent to Router A.

Figure 16-2. Debug All Updates from a Neighbor

Router A

interface loopback 1

 ip address 199.172.1.1 255.255.255.0

!

interface loopback 2

 ip address 199.172.2.1 255.255.255.0

!

interface loopback 3

 ip address 199.172.3.1 255.255.255.0

!

interface loopback 4

 ip address 199.172.4.1 255.255.255.0

!

router bgp 1

network 199.172.1.0

network 199.172.2.0

network 199.172.3.0

network 199.172.4.0

neighbor 172.17.1.1 remote-as 2

___________________________________________________________________________

Router B

interface loopback 1

 ip address 200.1.1.1 255.255.255.0

!

interface loopback 2

 ip address 200.1.2.1 255.255.255.0

!

interface loopback 3

 ip address 200.1.3.1 255.255.255.0

!

interface loopback 4

 ip address 200.1.4.1 255.255.255.0

!

router bgp 2

network 200.1.1.0

network 200.1.2.0

network 200.1.3.0

network 200.1.4.0

neighbor 172.17.1.2 remote-as 1

Verify that Routers A and B have formed a BGP neighbor relationship, and then debug BGP updates on Router B:

rtrB#debug ip bgp 172.17.1.2 updates

BGP updates debugging is on for neighbor 172.17.1.2

clear ip bgp 172.17.1.2



rtrB#

01:58:38: BGP(0): 172.17.1.2 computing updates, afi 0, neighbor version 0, table

 version 1, starting at 0.0.0.0

01:58:38: BGP(0): 172.17.1.2 update run completed, afi 0, ran for 0ms, neighbor

 version 0, start version 1, throttled to 1

01:58:39: BGP(0): 172.17.1.2 rcvd UPDATE w/ attr: nexthop 172.17.1.2, origin i,

 metric 0, path 1

01:58:39: BGP(0): 172.17.1.2 rcvd 199.172.1.0/24

01:58:39: BGP(0): 172.17.1.2 rcvd 199.172.2.0/24

01:58:39: BGP(0): 172.17.1.2 rcvd 199.172.3.0/24

01:58:39: BGP(0): 172.17.1.2 rcvd 199.172.4.0/24

01:59:09: BGP(0): 172.17.1.2 computing updates, afi 0, neighbor version 1, table

 version 9, starting at 0.0.0.0

01:59:09: BGP(0): 172.17.1.2 send UPDATE (format) 200.1.1.0/24, next 172.17.1.1,

 metric 0, path

01:59:09: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.2.0/24,

 next 172.17.1.1, metric 0, path

01:59:09: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.3.0/24,

 next 172.17.1.1, metric 0, path

01:59:09: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.4.0/24,

 next 172.17.1.1, metric 0, path

01:59:09: BGP(0): 172.17.1.2 1 updates enqueued (average=64, maximum=64)

01:59:09: BGP(0): 172.17.1.2 update run completed, afi 0, ran for 0ms, neighbor

 version 1, start version 9, throttled to 9

Example 2: Debug Specific Updates to and/or from a Particular Neighbor

For this example, debug only updates from Router A regarding network 199.172.3.0. Also debug the prefix 200.1.2.0 from Router B to Router A:

Router B

access-list 1300 permit 199.172.3.0 0.0.0.255

access-list 1300 permit 200.1.2.0 0.0.0.255



rtrB#debug ip bgp 172.17.1.2 updates 1300

BGP updates debugging is on for access list 1300 for neighbor 172.17.1.2



rtrB#clear ip bgp *

02:08:59: BGP(0): 172.17.1.2 rcvd UPDATE w/ attr: nexthop 172.17.1.2, origin i,

 metric 0, path 1

02:08:59: BGP(0): 172.17.1.2 rcvd 199.172.2.0/24

02:09:25: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.2.0/24,

 next 172.17.1.1, metric 0, path

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