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Ripng, and show ipv6 rip next-hops

Answered Question
Jan 14th, 2012
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Hi everybody



How is everybody doing ?


Please consider the following routing table:


R2#show ipv6 route

IPv6 Routing Table - 7 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

       U - Per-user Static route, M - MIPv6

       I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary

       O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

       ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2

       D - EIGRP, EX - EIGRP external

C   2000::/64 [0/0]

     via ::, Serial0/0

L   2000::1:2/128 [0/0]

     via ::, Serial0/0

R   2000:1::/64 [120/2]

     via FE80::C200:FFF:FE78:0, Serial0/0

C   2001::/64 [0/0]

     via ::, Serial0/0

L   2001::2/128 [0/0]

     via ::, Serial0/0

R   4000::/64 [120/2]

     via FE80::C200:FFF:FE78:0, Serial0/0

L   FF00::/8 [0/0]

     via ::, Null0

============================================================




R2#show ipv6 rip next-hops

RIP process "zee", Next Hops

  FE80::C200:FFF:FE78:0/Serial0/0 [4 paths]




My question is why the above output shows" 4 paths" ?  I can only see two routes that were learned via next hop FE80:c200:FF"FE78:0



Thanks and have a great weekend

Correct Answer by Peter Paluch about 5 years 7 months ago

Hi Sarah,


Apparently," show ipv6 rip next-hops" command gets its output from rib database not from routing table.


That's my understanding as well.


Next thing I noticed R1 advertised prefix 1111::/64  with metric 2 to R2.

But should the metric not be 1 as R1 and R2 are connected via serial interface ?


In RIPng, the metric is increased when receiving an update. This is in stern difference to previous RIP versions in which the metric was incremented when sending, and receiving routers simply accepted the metric without further incrementing it. Directly connected prefixes are advertised with initial hop count of 1 in Cisco's RIPng implementation, and after the receiving router increments the hop count by one, it yields the metric value of 2 you are seeing in your routing table.


Best regards,

Peter

Correct Answer by Peter Paluch about 5 years 7 months ago

Hi Sarah,


Can you please post the show ipv6 rip database output as well?


Best regards,

Peter

Correct Answer by lgijssel about 5 years 7 months ago

According to the command reference at:

http://www.cisco.com/en/US/docs/ios/ipv6/command/reference/ipv6_16.html#wp2669594


this would be: The number of routes in the IPv6 RIP routing table using the specified next hop


That would match exactly with your output, the only difference being that the keyword 'paths' is used instead.

Probably that is a matter of which IOS version you are using.


regards,

Leo


BTW: There is also an ipv6 related forum. Perhaps you can consider posting additional ipv6 questions there.

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Correct Answer
lgijssel Sat, 01/14/2012 - 08:46
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According to the command reference at:

http://www.cisco.com/en/US/docs/ios/ipv6/command/reference/ipv6_16.html#wp2669594


this would be: The number of routes in the IPv6 RIP routing table using the specified next hop


That would match exactly with your output, the only difference being that the keyword 'paths' is used instead.

Probably that is a matter of which IOS version you are using.


regards,

Leo


BTW: There is also an ipv6 related forum. Perhaps you can consider posting additional ipv6 questions there.

Correct Answer
Peter Paluch Sat, 01/14/2012 - 08:46
User Badges:
  • Cisco Employee,

Hi Sarah,


Can you please post the show ipv6 rip database output as well?


Best regards,

Peter

sarahr202 Sat, 01/14/2012 - 12:23
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  • Bronze, 100 points or more

Hi Peter


how are you doing?




I apologize for being late; I was recreating the set-up.



R1 s0/0---2001::/64--------s0/0R2


R1's


int loopback1

1111::1/64

ipv6 rip sarah enable



Below is the outputs of various commands on R2.


R2#show ipv6 route

IPv6 Routing Table - 4 entries


R   1111::/64 [120/2]

     via FE80::C200:5FF:FE74:0, Serial0/0

C   2001::/64 [0/0]

     via ::, Serial0/0

L   2001::2/128 [0/0]

     via ::, Serial0/0

L   FF00::/8 [0/0]

     via ::, Null0


R2#show ipv6 rip next-hops

RIP process "zee", Next Hops

  FE80::C200:5FF:FE74:0/Serial0/0 [2 paths]



R2#show ipv6 rip database

RIP process "zee", local RIB

1111::/64, metric 2, installed

     Serial0/0/FE80::C200:5FF:FE74:0, expires in 159 secs

2001::/64, metric 2

     Serial0/0/FE80::C200:5FF:FE74:0, expires in 159 secs

=========================================

Apparently," show ipv6 rip next-hops" command gets its output from rib database not from routing table.


Next thing I noticed R1 advertised prefix 1111::/64  with metric 2 to R2.

But should the metric not be 1 as R1 and R2 are connected via serial interface ?


I also noticed even though R1 and R2 are connected via serial interface which is configured with 2001::/64,R1 still advertises the prefix 2001::/64 to R2.

Had R1 and R2 been configured for ipv4, R1 would not have advertised  2001:: /64 to R2.


Thanks and have a great weekend

Correct Answer
Peter Paluch Sun, 01/15/2012 - 01:26
User Badges:
  • Cisco Employee,

Hi Sarah,


Apparently," show ipv6 rip next-hops" command gets its output from rib database not from routing table.


That's my understanding as well.


Next thing I noticed R1 advertised prefix 1111::/64  with metric 2 to R2.

But should the metric not be 1 as R1 and R2 are connected via serial interface ?


In RIPng, the metric is increased when receiving an update. This is in stern difference to previous RIP versions in which the metric was incremented when sending, and receiving routers simply accepted the metric without further incrementing it. Directly connected prefixes are advertised with initial hop count of 1 in Cisco's RIPng implementation, and after the receiving router increments the hop count by one, it yields the metric value of 2 you are seeing in your routing table.


Best regards,

Peter

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