1. BGP in practice Sabri Berisha sabri@cluecentral.net What The Hack 2005

2. bgp in practice - cluecentral Introduction Sabri Berisha, sabri@cluecentral.net http://www.cluecentral.net/wth/ This presentation is written by me. Permission is hereby granted to copy, distribute and/or modify this presentation with or without useless copyright notices containing my name.

3. bgp in practice - cluecentral Today Opening Short review of Megabit 2003 Advanced topics How to play with BGP Useful links and tips Easter egg

4. bgp in practice - cluecentral Questions? Please do raise your hand if you do not understand what I am talking about. Feel free to ask anything besides my PIN-code. General knowledge of TCP/IP and internet-routing is expected.

5. bgp in practice - cluecentral Megabit 2003 BGP4 – ipv4 unicast routes Using zebra for BGP Test-setup using Cisco routers Filters, filters, filters

6. bgp in practice - cluecentral Advanced topics Introduction on BGP attributes Local preferences Multiple Exit Descriminators (MED’s) Decision algorithm Communities Traffic engineering

7. bgp in practice - cluecentral BGP attributes Next-hop address of next-hop gateway Local-pref preference within AS As path neighboring and transit networks Origin originator (igp, egp, incomplete) Med multiple exit descriminator Community community value

8. bgp in practice - cluecentral Local preferences Localpref is set AS-wide Localpref is the most important tool for traffic-engineering Setting localpref using a Juniper Networks JunOS-driven router Setting localpref using a Cisco Systems IOS-driven router

9. bgp in practice - cluecentral Multiple Exit Descriminators Optional non-transive attribute: not necessary, but if set it MAY NOT be readvertised to other peers Setting MED’s using a Juniper Networks JunOS-driver router Setting MED’s using a Cisco Systems IOS-driven router

10. bgp in practice - cluecentral BGP decision algorithm Varies per vendor, but common: –Next-hop reachability –Localpref –Shortest AS-path length –Origin: IGP, EGP, Incomplete/Unknown –MED –eBGP peer vs iBGP peer –Router-ID –Peer-ID

11. bgp in practice - cluecentral Communities Optional transitive (not necessary, may be reannounced to other peers) Communities give the network engineer the opportunity to distinguish prefixes received from multiple peers with the same as- path length

12. bgp in practice - cluecentral Communities (2) Setting communities using a Juniper Networks JunOS-driven router Setting communities using a Cisco Systems IOS-driven router Document your communities so everyone benefits from them

13. bgp in practice - cluecentral Advanced traffic-engineering Learn the trick: use communities and local-pref to determine how the traffic flows through your network Cold or hot potato? Examples

14. bgp in practice - cluecentral How to play with BGP Various options: –Install your favorite *nix and install Quagga –Install your favorite *nix and install OpenBGPD –Work for an ISP :-)

15. bgp in practice - cluecentral Useful links and tips Filter your peers http://www.bgp4.as/ Filter your peers http://www.virt-ix.net/ Filter your peers http://www.occaid.org/ Did I mention you should filter your peers?

16. bgp in practice - cluecentral Easter Egg The truth is out there.