To avoid the need for yet another BGP implementation, Super Sparrow accesses BGP information by querying route servers. A route server is a router, or host running a routing daemon, that may be queried for the preferred prefix for a IP address. The current implementation supports three different route servers: GNU Zebra[14] and GateD[17], routing daemons that run on a variety of platforms including Linux10, and Cisco IOS[4], the operating system that runs on Cisco routers and is synonymous with BGP and routing in general.
The current implementation uses telnet access to route servers to query the preferred prefix for an IP address. The tenet interface to route servers is generally intended for manual interaction with the route server but provides a reasonably fast and portable way of other programmes accessing the route server. A sample session with GNU Zebra to determine the preferred prefix for 192.168.193.15 from a route server running on 192.168.192.13 is given in figure 5.
The results shown in the figure indicate that there are two prefixes for the query made and that the second prefix listed is preferred. The AS path for the preferred prefix is 64702. It is the AS path of the preferred prefix that Super Sparrow uses to determine if a point of presence in the Super Sparrow network is closer to the address begin queried than the route server being queried as described in section 3.3.
$ telnet 192.168.192.13 bgpd
Trying 192.168.192.13...
Connected to 192.168.192.13.
Escape character is '^]'.
Hello, this is zebra (version 0.89.horms.pre.2)
Copyright 1996-2000 Kunihiro Ishiguro
User Access Verification
Password:
jasmine> sho ip bgp 192.168.193.15
BGP routing table entry for 192.168.193.0/24
Paths: (2 available, best #2, table Default-IP-Routing-Table)
64600 64601 64602
192.168.192.12 from 192.168.192.12 (192.168.192.12)
Origin IGP, metric 1, localpref 100, valid, external
Last update: Fri Oct 6 15:47:28 2000
64702
192.168.193.11 from 192.168.193.11 (192.168.193.11)
Origin IGP, metric 1, localpref 100, valid, external, best
Last update: Fri Oct 6 15:44:05 2000
jasmine> exit
Connection closed by foreign host.
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