From CCIE Study Wiki
BGP Synchronization is a solution to guarantee that all needed routes for BGP routing existed in non-BGP routers.
Theory
Synchronization is a legacy solution to the problem of internal routers not running BGP would not have BGP routes in their routing table, and any traffic sent via BGP routes from other BGP-enabled routes would not have any destinations, creating a "black hole".
The original solution to this problem involved redistributing these routes into the IGP and enabling BGP synchronization, guaranteeing all needed routes existed in the non-BGP routers. Today, running BGP on all routers, BGP route reflectors, or BGP confederations are more often used to solve these issues.
In order to add a BGP route to the IP routing table, the route must be the best BGP route and must have the lowest AD in comparison with routes from other sources. In addition, iBGP routes may have to be synchronized (sync).
- Sync provides an additional rule for an iBGP route to be considered best - the exact prefix had to have been learned via an IGP and has to currently exist in the routing table.
- Sync is off by default
Commands
Default Settings
Verification
Troubleshooting, Tips, and Tricks
- When using sync with OSPF as the IGP - OSPF and BGP RIDs must be the same for sync to consider a route to be best.
Online Resources
Have something to contribute? See a mistake on this page? Have a hint or a link to share?
The CCIE Study Wiki is open to everyone to edit! All you need to do is to create an account to start contributing.
Please be sure to follow our posting guidelines when editing the wiki.
Maybe you have just have some thoughts or suggestions for this entry?
Use the Discussion link on the top or bottom menu to create or join the CCIE forum post on this topic.
You can also go straight to the CCIE Forums and start a new discussion in the forum of your choice.
If you'd rather just contact us with your thoughts, we'd love to hear what you have to say.