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Candidate Bootstrap-RP with TTL value of 1

Hi All,

Going through Bootstarap-RP functioning I've found that the candidate Bootstarp-RP's send Bootstarap messages to the multcast address 224.0.0.13 with a TTL value of 1. If the bootstarp message is used to elect the BSR in the network , how can the TTL value of the Bootstrap message can be 1 ? Soppose routers are connected in this way A <--> B <--> C <--> D How will the router D receive the Bootstrap message sent by router A because it will be dropped by router B because if TTL expiration.

Thanks in Advance

Regards

Umesh Shetty

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Cisco Employee

Candidate Bootstrap-RP with TTL value of 1

Hello Umesh,

If the bootstarp message is used to elect the BSR in the network , how can the TTL value of the Bootstrap message can be 1 ?

This is similar to OSPF and flooding of LSAs. The LSU packets that carry LSAs are also sent with the TTL=1. However, if a router receives an LSU, it extracts LSAs, stores them in its LSDB and then packages the received LSAs into a new packet and forwards them over all other interfaces. In other words, it is the contents of the packets that are flooded, not entire packets, and the IP header of the packets is recreated at each router.

With the Bootstrap messages, it is the same. After receiving a Bootstrap message, its contents are forwarded further in new IP packets but the packets themselves are not flooded. This prevents packets from looping through the network while allowing for dissemination of the message contents to all routers.

Would this answer your question?

Best regards,

Peter

2 REPLIES
Cisco Employee

Candidate Bootstrap-RP with TTL value of 1

Hello Umesh,

If the bootstarp message is used to elect the BSR in the network , how can the TTL value of the Bootstrap message can be 1 ?

This is similar to OSPF and flooding of LSAs. The LSU packets that carry LSAs are also sent with the TTL=1. However, if a router receives an LSU, it extracts LSAs, stores them in its LSDB and then packages the received LSAs into a new packet and forwards them over all other interfaces. In other words, it is the contents of the packets that are flooded, not entire packets, and the IP header of the packets is recreated at each router.

With the Bootstrap messages, it is the same. After receiving a Bootstrap message, its contents are forwarded further in new IP packets but the packets themselves are not flooded. This prevents packets from looping through the network while allowing for dissemination of the message contents to all routers.

Would this answer your question?

Best regards,

Peter

New Member

Candidate Bootstrap-RP with TTL value of 1

Thanks Peter, That solves the query !!!

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