Net Worker World

http://wiki.nil.com/AS-path_prepending_(technical_details ) http://ciscodreamer.blogspot.com/2009/07/bgp-as-path-prepending.html

Local Preference Attribute The local preference attribute is used to prefer an exit point from the local autonomous system (AS). Unlike the weight attribute, the local preference attribute is propagated throughout the local AS. If there are multiple exit points from the AS, the local preference attribute is used to select the exit point for a specific route. The default value for local preference is 100. with default local preference, let's take a look the output from R3, we can see R3 recevies the route of 192.168.12.0/24 from two paths, the interesting thing is that the path from 172.16.13.1 which is R1 has no Local Preference value displayed, the route from R4 (4.4.4.4) does have default Local Preference value 100. But when take a look closer, we can see both path have default value 100. R3>sh ip bgp 192.168.12.0/24 BGP routing table entry for 192.168.12.0/24, version 19 Paths: (2 available, best #2, table Default-IP-Routing-Table, not advertised to EBGP peer) Advertised to

The BGP local-as command has several keywords, this test is trying to clarify how to use them. According to Cisco documentation, this command is to support Dual AS configuration for network AS migration. Here we are assuming R2 is ISP and is planing to migrate from AS 200 to AS 2000. R3 is R2's customer, R1 is another ISP where we will check and verify if R2 AS# migration causes problem. 1. local-as without any other keywords. R2#sh run s bgp router bgp 200 no synchronization bgp log-neighbor-changes neighbor 10.10.12.1 remote-as 100 neighbor 10.10.23.3 remote-as 300 neighbor 10.10.23.3 local-as 2000 no auto-summary R2# hmm, got error: *Mar 1 02:24:26.247: %BGP-3-NOTIFICATION: received from neighbor 10.10.23.3 2/2 (peer in wrong AS) 2 bytes 07D0 looks R2 is using the local-AS command AS# instead of the bgp process AS# to talk to peer R3. Let's change R3 to use remote-as# 2000 for now. R3#sh run s bgp router bgp 300 no synchronization bgp log-neighbor-changes network 192.168.10.

Server A and Server B are in different VLANs on the CSS, if interfaces and circuit VLANs are configured properly, then Server A needs to talk to Server B or vice versa, what other configuration is needed on CSS? do we need VIP and Soruce Group? The answer is: the CSS by default routes traffic between VLANs, so no VIP or Group configuration is needed.

iBGP is running between routers in same sub-AS, eBGP is running between different sub-AS. However, when BGP calculate bset path, it doesn't treat them as real iBGP and eBGP R4 received route to 200.200.200.8/29 which is in AS 200 from both AS100 eBGP router and iBGP router in sub AS64526. Path going through AS100 seems a shorter, but according to Cisco documentation, confederation AS_CONFED_SEQUENCE doesn't take account when BGP select best path. http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml we can see R4 choose internal router R5 as the best path to 200.200.200.8/29 What the relationship between R2 and R4, they are both RR for redundancy. The IPExpert video configured them as RR-Client to each other, is this correct or doesn't matter? searched Internet seems most example they are just regular iBGP peers. If they configured as RR-client to each other, when R4 received a route 200.200.200.32/28 from AS 100, it sent to R2, since R2 des

Have been a networker for years, didn't take any action to pursue a CCIE certificate until recently, one reason is that I think CCIE doesn't mean everything for a networker. Be a good networker , we definitely need more knowledge than Cisco stuff and more experiences of dealing with real world chanllenges. I changed my mind and on the jounrney of CCIE R&S now. Time is an issue to me as I have a busy work and a 17 months old little girl at home. Plan to take my first try at the end of 2010. I have IPExpert selfstudy materials and some PDF books. I know I will be really busy for at least half year. :) Jason