Sunday, April 23, 2017

Looking-glass

BGP is the routing protocol of the Internet. Many of the major service providers allow
anonymous Telnet into route servers that act just like Cisco routers. Do an Internet search for the term “looking-glass routers,” and you should find plenty of links. These route servers are an excellent way to learn more about BGP, as they are a part of the largest network in the world and have active routes to just about every public network on Earth. Unless you’re working at a tier-1 service provider, where else could you get to poke around with a BGP router that has 20 neighbors, 191,898 prefixes, and
3,666,117 paths? I have a pretty cool lab, but I can’t compete with that! Here is the output from an actual route server:

route-server>sho ip bgp summary

BGP router identifier 10.1.2.5, local AS number 65000
BGP table version is 208750, main routing table version 208750
191680 network entries using 19359680 bytes of memory
3641563 path entries using 174795024 bytes of memory
46514 BGP path attribute entries using 2605064 bytes of memory
42009 BGP AS-PATH entries using 1095100 bytes of memory
4 BGP community entries using 96 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 197854964 total bytes of memory


Choose your favorite public IP network (doesn’t everyone have one?) and see how the
paths look from the looking-glass router. If you don’t have a favorite, choose one that
you can easily figure out, like one in use by www.cisco.com or www.oreilly.com:

[bossman@myserver bossman]$nslookup www.oreilly.com

Server: localhost
Address: 127.0.0.1
Name: www.oreilly.com
Addresses: 208.201.239.36, 208.201.239.37
Once you have the address, you can do a lookup for the network:
route-server>sho ip bgp 208.201.239.0
BGP routing table entry for 208.201.224.0/19, version 157337




Looking Glass Sites
You can access a Looking Glass (LG) server remotely to view routing information. They are servers on the Internet that run Looking Glass software that is available to the public. The servers are essentially read-only portals to the router belonging to the organizations  running them. They are basically just providing a ping or traceroute from a remote location for you.



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