Unanswered Question
Dec 17th, 2009
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I have a ring of 8 routers in a ring runing OSPF , can detect LOS ,so I want to implement RSVP TE with FRR.

One Hop.JPG

For Traffic going from R1 to R4, it will use the Primary Tunnel R1--R2 and then r3, and finally arrive r4. If link between R1--R2 fails, will the traffic quickly move to Backup NNhop tunnel ( as shown in diagram) and hence the user traffic which was sourced behind R1 and wanted to reach destination behind r4 will follow this path r1--r8---r7---r6---r5---r4---r3-----r2-----r3---r4 . As I understand that the Primary FRR & Backup TE Tunnel will have same destination ( its mandatory.. right ?). This creates unwanted traffic on R4--R3--R2 long as the R1--R2 link is down.

Is this the design problem with One hop tunnel.. ?

My friend say after link failure on R1--R2, IGP convergence will take place and this unwanted  upstream movement of user traffic will stop. He couldn't explain why ?

Can somebody explain ...



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shivlu jain Thu, 12/17/2009 - 22:56
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On failure of R1-R2 link, traffic will follow the backup tunnel. There will not be unwanted traffic on R3-R2 because the backup tunnel is from R4 to R1 via R8. So don't worry about that designers have already taken care about that.


shivlu jain

gauravprakash Fri, 12/18/2009 - 00:41
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Hi Shivlu,

Thx , perhaps I did not get that ....The primary tunnel is one hop tunnel and my backup tunnel is multi hop away ( may be I shud not use NNHOP earlier )..I guess the backup Tunnel shud have the same destination as Primary , so it will traverse all the ring ( other way) and then reach R2 , then move towards R4. So there is  extra traffic from R4----R3---R2 while the traffic ( source behind R1 & destination behind R4 ) is moving to the end of Backup tunnel. From end of backup tunnel .. anyways it has to come down to R4..


Gaurav Prakash


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