First of all, may I welcome you to my site. My name is Chris and I'm from the UK and work as a Systems Engineer for Cisco. This blog was initially created to post up my subnetting technique but has now got more stuff to do with attaining Cisco certifications. Either way I really hope that the content is sufficent for your needs and I look forward to hearing your feedback. If you find that the content really helps you please feel free to donate using the PayPal link on the right.

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CCIE - Warm-Up Phase - BGP


I am pretty happy with BGP but still there are a few things that I need to get into my head.

7.5 - Disable Connected Check - this allows eBGP peers to use an IP address to peer that is not directly connected to the neighbor (e.g. a loopback interface). The difference between this and ebgp-multihop is that the TTL is not adjusted for disable-connected-check and that eBGP sessions will not form over transit routers.

7.8 - The bgp cluster-id is applied to the route reflector only.

7.9 - The confederation AS is used in the "router bgp" command and the bgp-confederation identifier refers to the proper AS. You must also specify bgp confederation peers otherwise the adjacency won't come up. In addition, confederation peers are treated as eBGP neighbors and should use directly connected interfaces, otherwise need to use things like update-source and ebgp-multihop.

7.11 - Instead of using next-hop-self you can create a route-map to "set ip next-hop" and apply that to the neighbor (e.g. neighbor route-map ROUTE_MAP_NAME in/out"

7.12 - iBGP synchronization - Do not advertise a BGP route unless it is also learned by the IGP running in the network. In essence this requires the edge router to redistribute the eBGP routes into the IGP in order for iBGP to advertise the routes. Be careful when redistributing routes into IGP. Use an AS PATH access-list:

ip as-path access-list 1 permit ^_54
route-map MATCH_AS_PATH permit 10
match as-path 1
router eigrp 100
redistribute bgp 100 metric 100000 1000 255 1 1500 route-map MATCH_AS_PATH

Posted byChris Bloomfield at 08:52  


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