Graceful Restart Example

When A has finished advertising its RIB, any marked routes which weren’t replaced are flushed.

B and C send their routes to A. A stores them in its RIB.

BGP halts on A. B and C’s RIBs and A’s FIB all mark routes for later deletion.

BGP comes back up and establishes new sessions with B and C.

RIB:

(routes from A)

(other routes)

RIB:

(routes from A)

(other routes)

RIB:

(routes from A)

(other routes)

RIB:

(routes from A)

(other routes)

RIB:

(new routes from A)

(other routes)

RIB:

(new routes from A)

(other routes)

Router A

Router B

Router C

RIB:

(routes from B)

(routes from C)

RIB:

(routes from B)

RIB:

FIB:

(routes from B)

(routes from C)

FIB:

(routes from B)

(routes from C)

FIB:

(new routes from B)

(new routes from C)

RIB:

(routes from B)

(routes from C)

Once B and C have sent all their routes, A runs best path, populates its FIB

… and advertises its new RIB, replacing the marked routes.