BGP Tutorial for ISP customers – Controlling outbound traffic

Outbound traffic control is actually easier than you thought. If you have single ISP link, all outbound traffic will obviously exit out the link. As I mentioned earlier, if you have single ISP link then you don’t really need BGP. Probably you may have more questions, if you have more than two ISP links. Redundanacy and load-sharing would be biggest concerns.

 

• BGP Tutorial for ISP customers – Do I need BGP?
• BGP Tutorial for ISP customers – Own ASN or borrowing one.
• BGP Tutorial for ISP customers – Enough memory for full routes?
• BGP Tutorial for ISP customers – Controlling outbound traffic.
• BGP Tutorial for ISP customers – Controlling inbound traffic.
• BGP Tutorial for ISP customers – Configuring BGP.
• BGP Tutorial for ISP customers – BGP community string from ISP.
• BGP Tutorial for ISP customers – Verifying BGP routes.
• BGP Tutorial for ISP customers – BGP Troubleshooting.

 

 

Still default route is needed as receiving full BGP routing table?

Yes, Tier1 ISP’s full BGP routing table would cover most of routes, but not 100%. So, we are strongly recommending configuring default route on your router or receiving default route from ISP.

 

Single ISP link

Nothing to consider. Just put a default route or ask your ISP to provide default route thru BGP routing table.

 ex) Cisco_Router(config)#ip route 0.0.0.0 0.0.0.0 x.x.x.x (WAN IP on other side of interface)

 

Two ISP links on same router

If you want to load-sharing outbound traffic, simply setup default route pointing to both ISP link. It will make about 50/50 traffic sharing. (It won’t exact 50/50 due to traffic is flowing per destination, but not per packet). Also, it provides redundancy as well.

ex) Cisco_Router(config)#ip route 0.0.0.0 0.0.0.0 x.x.x.x (ISP "A" WAN IP on other side of interface)
     Cisco_Router(config)#ip route 0.0.0.0 0.0.0.0 y.y.y.y (ISP "B" WAN IP on other side of interface)

 

Three ISP links on same router

Yes, it is same as above case.

ex) Cisco_Router(config)#ip route 0.0.0.0 0.0.0.0 x.x.x.x (ISP "A" WAN IP on other side of interface)
     Cisco_Router(config)#ip route 0.0.0.0 0.0.0.0 y.y.y.y (ISP "B" WAN IP on other side of interface)
     Cisco_Router(config)#ip route 0.0.0.0 0.0.0.0 z.z.z.z (ISP "C" WAN IP on other side of interface)

 

Two ISP links on two different routers

I guess many eCommerce user has this network layout. No simple way to make load-sharing and redundancy at the same time. However, still there is way to do it.

See our BGP configuration examples at topology 5