Com*One BGP FAQ

1. What is BGP?
2. How does BGP work?
3. Do I need BGP?
4. What do I need to set up BGP?
5. What is an Autonomous System?
6. What is an Autonomous System Number (AS#)?
7. What does multi-homed mean?
8. Can you show me a sample configuration?

Q.) What is BGP?

A.) BGP stands for Border Gateway Protocol. Border Gateway Protocol (BGP) is a routing protocol most commonly used between autonomous systems. BGP is a dynamic routing protocol that exchanges routes between BGP neighbors (sometimes called "peers") .

Q.) How does BGP work?

A.) In simplest terms, BGP learns routes from your internal routing protocol (static routes, EIGRP, RIP, OSPF etc.) and announces them to a BGP-speaking neighbor or peer (the TelOne router in this case) . This means that if you are running BGP, you are responsible for your own routing and announcements. TelOne routers learn about your network from your router. Unless you announce the route to us, we cannot send you traffic for that CIDR block. A route announcement is sometimes referred to as a 'prefix'. A prefix is composed of a path of AS numbers, indicating which networks the packet must pass through, and the IP block that is being routed, so a BGP prefix would look something like: 5713 8668 209.88.88.0/21. The /21 part is referred to as a CIDR mask. The /21 indicates that there are 21 ones in the netmask for this block starting from the left hand side. A /21 corresponds to the natural mask 255.255.248.0.

Q. Do I need BGP?

A. No unless you are connected to more than one Internet Provider. Static routing is acceptable for most applications, including load balancing.

Q. What do I need to set up BGP?

A. To set up BGP, you need a router capable of running BGP (a Cisco router with 10.3 or later IOS will do), an Autonomous System Number from ARIN, and you must also be multi-homed. Once you have all this, contact TelOne at adm-bgp4@telone.co.zw to request the setup of BGP.

Q. What is an Autonomous System?

A. An autonomous system is one network or series of networks that are all under one administrative control.

Q. What is an Autonomous System Number?

A. An autonomous system number uniquely identifies an autonomous system. These numbers are controled by ARIN, and cannot be randomly selected or configured yourself. You must receive an AS number from ARIN before you can start running BGP.

Q. What does "multi-homed" mean?

A. You are "multi-homed" if your network is directly connected to two or more ISP's.

Q. Can you show me a sample configuration?

A. While the same configuration may not work for all customers, we can provide a list of configuration statements for you to try. For a list of configuration tasks see Cisco's Configuring BGP page.

Cisco router configuration commands for BGP:
ip subnet-zero
router bgp [ your AS #]
 no synchronization
 network [ IP block  ]
 redistribute [ static | ospf | rip ]
 neighbor [ TelOne IP Add ] remote-as [ TelOne AS# ]
 neighbor [ TelOne IP Add ] version 4
 neighbor [ TelOne IP Add ] distribute-list xx out
 no auto-summary

 ip classless

(distribute list configuration statements)
 access-list xx permit [your IP block][inverse mask] 
 access-list xx permit (remaining statements)

 ip route [ address ] [ mask ] ethernet 0

Please see our online BGP policy document for additional information.