From: Mohamed T. Kondela (mtaib@sagia.gov.sa)
Date: Mon Jan 22 2007 - 17:16:55 ART
I missed the sh ip route and sh ip bgp <prefix>
1) Rack1R5#sh ip route
D EX 204.12.1.0/24 [170/2738176] via 183.1.105.10, 07:11:54,
FastEthernet0/0
C 183.1.105.0 is directly connected, FastEthernet0/0
<output truncated>
2) Rack1R5#sh ip bgp 28.119.16.0/24
BGP routing table entry for 28.119.16.0/24, version 35
Paths: (2 available, best #1, table Default-IP-Routing-Table)
Advertised to update-groups:
1 2
54, (Received from a RR-client)
54.1.1.254 (metric 20) from 183.1.46.6 (150.1.6.6)
Origin IGP, metric 0, localpref 100, valid, internal, best
54, (Received from a RR-client)
204.12.1.254 (metric 2738176) from 183.1.0.3 (150.1.3.3)
Origin IGP, metric 0, localpref 100, valid, internal
Regards
Mohamed T. Kondela
Senior Network Engineer
IT Dept.
Fax: 4473037 x 303
mtaib@sagia.gov.sa
Saudi Arabian General Investment Authority
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-----Original Message-----
From: Mohamed T. Kondela
Sent: Monday, January 22, 2007 11:11 PM
To: 'Brian McGahan'; Cisco certification
Subject: RE: How BGP verify Next-hop
1)Rack1R5#sh ip bgp
Network Next Hop Metric LocPrf Weight Path
*>i28.119.16.0/24 54.1.1.254 0 100 0 54 i
* i 204.12.1.254 0 100 0 54 i
2) Rack1R5#sh ip route 204.12.1.254
Routing entry for 204.12.1.0/24
Known via "eigrp 100", distance 170, metric 2738176, type external
Redistributing via eigrp 100, ospf 1
Advertised by ospf 1 subnets
Last update from 183.1.105.10 on FastEthernet0/0, 06:59:40 ago
Routing Descriptor Blocks:
* 183.1.105.10, from 183.1.105.10, 06:59:40 ago, via FastEthernet0/0
3) Rack1R5#sh ip route 183.1.105.10
Routing entry for 183.1.105.0/24
Known via "connected", distance 0, metric 0 (connected, via interface)
4) Rack1R5#sh ip bgp neigh 150.1.4.4 advertised-routes
Network Next Hop Metric LocPrf Weight Path
*>i28.119.16.0/24 54.1.1.254 0 100 0 54 i
5) Rack1R5#ping 204.12.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 204.12.1.3, timeout is 2 seconds:
!!!!!
6) Rack1R5#ping 204.12.1.254
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 204.12.1.254, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
The fact is that no routing protocol between BB3 and R3 , but still R5
recursing for 204.12.1.254 (?). the subnet has been redistributed in R3.
Regards
-----Original Message-----
From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
Sent: Monday, January 22, 2007 10:46 PM
To: Mohamed T. Kondela; Cisco certification
Subject: RE: How BGP verify Next-hop
Post the "show ip route" and "show ip bgp" output along with the "show
ip route w.x.y.z" and "show ip bgp w.x.y.z" for the prefix.
HTH,
Brian McGahan, CCIE #8593 (R&S/SP)
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987 x 705
Outside US: 775-826-4344 x 705
24/7 Support: http://forum.internetworkexpert.com
Live Chat: http://www.internetworkexpert.com/chat/
-----Original Message-----
From: Mohamed T. Kondela [mailto:mtaib@sagia.gov.sa]
Sent: Monday, January 22, 2007 1:36 PM
To: Brian McGahan; Cisco certification
Subject: RE: How BGP verify Next-hop
BMC, I thought the exact same way. But in reality, I experienced some
trouble. The subnet was reachable (where the Next-hop resides) but not
the next-hop, due to some distribute-list or lack of IGP..
Due to subnet reachability, all routers are recursing the route (show ip
route <next-hp>) to an interface right. But the BGP process is not
advertising the prefix to its neighbor due to inaccessible Next-hop.
Yes, I am exactly pointing to a issue in IEWB 4.0 Lab 1 BGP..:)
Regards
Mohamed T. Kondela
Senior Network Engineer
IT Dept.
Fax: 4473037 x 303
mtaib@sagia.gov.sa
Saudi Arabian General Investment Authority
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-----Original Message-----
From: Brian McGahan [mailto:bmcgahan@internetworkexpert.com]
Sent: Monday, January 22, 2007 10:20 PM
To: Mohamed T. Kondela; Cisco certification
Subject: RE: How BGP verify Next-hop
It's based on whether route recursion can occur to an interface.
When you learn a BGP route it will say "via w.x.y.z" in the routing
table. The router internally says "show ip route w.x.y.z" to see if
there is a match, and what the outgoing interface is. The route
recursion process happens until the outgoing interface is found. If the
next-hop cannot be recursed bestpath selection cannot continue and the
BGP route cannot be used.
HTH,
Brian McGahan, CCIE #8593 (R&S/SP)
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987 x 705
Outside US: 775-826-4344 x 705
24/7 Support: http://forum.internetworkexpert.com
Live Chat: http://www.internetworkexpert.com/chat/
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Mohamed T. Kondela
Sent: Monday, January 22, 2007 1:09 PM
To: Cisco certification
Subject: How BGP verify Next-hop
Any idea what method is used by BGP to verify the next-hop reachability
? How does a BGP router know that the next hop is reachable or not?
Icmp?
Show ip route x.x.x.x ?
I am just trying to know what exactly they are doing in the back ground.
Regards
Mohamed T. Kondela
Senior Network Engineer
IT Dept.
Fax: 4473037 x 303
mtaib@sagia.gov.sa
Saudi Arabian General Investment Authority
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This message contains confidential information and is intended only for
the individual named. If you are not the named addressee you should not
disseminate, distribute or copy this e-mail. Please notify the sender
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delete this e-mail from your system. E-mail transmission cannot be
guaranteed to be secure or error-free as information could be
intercepted, corrupted, lost, destroyed, arrive late or incomplete, or
contain viruses. The sender therefore does not accept liability for any
errors or omissions in the contents of this message, which arise as a
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request a hard-copy version.
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