BGP in practice Sabri Berisha What The Hack 2005

bgp in practice - cluecentral Introduction Sabri Berisha, 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.

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

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.

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

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

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

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

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

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

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

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

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

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 :-)

bgp in practice - cluecentral Useful links and tips Filter your peers Filter your peers Filter your peers Did I mention you should filter your peers?

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