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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. 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 BGP Updates

In Figure 16-4, Router A is advertising four prefixes to Router B, and Router B is advertising four prefixes to Router A. Debug all the updates on Router B.

Figure 16-4. 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



rtrB#debug ip bgp updates

BGP updates debugging is on

rtrB#clear ip bgp *

2d03h: BGP(0): 172.17.1.2 send UPDATE (format) 200.1.1.0/24, next 172.17.1.1,

 metric 0, path

2d03h: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.2.0/24,

 next 172.17.1.1, metric 0, path

2d03h: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.3.0/24,

 next 172.17.1.1, metric 0, path

2d03h: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.4.0/24,

 next 172.17.1.1, metric 0, path

2d03h: BGP(0): 172.17.1.2 1 updates enqueued (average=64, maximum=64)

2d03h: BGP(0): 172.17.1.2 update run completed, afi 0, ran for 0ms, neighbor

 version 0, start version 5, throttled to 5

2d03h: BGP(0): 172.17.1.2 rcvd UPDATE w/ attr: nexthop 172.17.1.2, origin i,

 metric 0, path 1

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.1.0/24

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.2.0/24

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.3.0/24

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.4.0/24

Example 2: Debug Input Updates

Debug BGP updates on Router B for routes received from Router A.

rtrB#debug ip bgp updates in

BGP updates debugging is on (inbound)

rtrb#clear ip bgp *

2d03h: BGP(0): 172.17.1.2 rcvd UPDATE w/ attr: nexthop 172.17.1.2, origin i,

 metric 0, path 1

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.1.0/24

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.2.0/24

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.3.0/24

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.4.0/24

Example 3: Debug Output Updates for Specific Prefixes Sent to All BGP Neighbors

Debug BGP updates on Router B for local prefixes 200.1.2.0 and 200.1.3.2:

Router B

access-list 1 permit 200.1.2.0 0.0.1.255



rtrB#debug ip bgp updates 1 out

BGP updates debugging is on for access list 1 (outbound)

rtrB#clear ip bgp *

2d03h: BGP(0): nettable_walker 200.1.2.0/24 route sourced locally

2d03h: BGP(0): nettable_walker 200.1.3.0/24 route sourced locally

2d03h: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.2.0/24,

 next 172.17.1.1, metric 0, path

2d03h: BGP(0): 172.17.1.2 send UPDATE (prepend, chgflags: 0x208) 200.1.3.0/24,

 next 172.17.1.1, metric 0, path

Example 4: Debug Input Updates for Specific Prefixes Received from a Specific BGP Neighbor

Debug updates for prefixes 199.172.2.0 and 199.172.3.0 received from Router A:

Router B

access-list 2 permit 199.172.2.0 0.0.1.255



rtrB#debug ip bgp in 172.17.1.2 updates 2

BGP updates debugging is on for access list 2 for neighbor 172.17.1.2 (inbound)

rtrB#clear ip bgp *

p2#

2d03h: BGP(0): 172.17.1.2 rcvd UPDATE w/ attr: nexthop 172.17.1.2, origin i,

 metric 0, path 1

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.2.0/24

2d03h: BGP(0): 172.17.1.2 rcvd 199.172.3.0/24

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