Embedded RP Address Questions

[gongya001]

1. Can any valid RP address be converted to be Embedded RP address ? such as 2001:1:2:3:4:5:6:8/64.

2. Can 2005::5:5:5:5/128 be converted to be embedded RP address ?  If yes, assume group is 10, should it be 2005:5:5:5::10 or something else?

3: if in a network with prefix 2001:1:2:3::/64, there are two nodes, one is 2001:1:2:3::1:1 and the other is 2001:1:2:3::2.1, what embedded RP should be for them ?

I did read something from https://ieoc.com/discussion/12600/ipv6-embedded-rp, but still confused.

thanks !!

[Harold Ritter · Accepted solution]

1- Per RFC3956, you can specify the first 64 bits (max) of the RP address and the last 4 bits (RIID) only as part of the embedded RP address.

2- As per previous answer, you can only specify the first 64 bits and last 4 bits, therefore RP address 2005::5:5:5:5 could not be used for an embedded RP multicast group. On the other hand 2005:5:5:5::5 could.

3- 2001:1:2:3::1:1 and 2001:1:2:3::2:1 do not comply either to the rules stated in RFC3956. 2001:1:2:3::1 and 2001:1:2:3::2 do and would look something like this:

2001:1:2:3::1 = FF7E:140:2001:1:2:3::<32 bits for group-id>

2001:1:2:3::2 = FF7E:240:2001:1:2:3::<32 bits for group-id>

Embedded RP multicast group address format from RFC3956:

|   8    |  4 |  4 |   8    | 8  |       64       |    32    |
+--------+----+----+--------+----+----------------+----------+
|11111111|flgs|scop|reserved|plen| network prefix | group ID |
+--------+----+----+--------+----+----------------+----------+

https://tools.ietf.org/html/rfc3956

Regards,

[gongya001]

thanks so much for clarification!!

[gongya001]

From <https://mellowd.co.uk/ccie/?p=3235>, I got the following, I tested it, I could not get the same result.

interface FastEthernet0/0
 ipv6 mld join-group FF75:180:3000:1111::1

R4#show ipv6 mroute | beg \(
(*, FF75:180:3000:1111::1), 00:05:22/never, RP 3000:1111::1, flags: SCLJ
  Incoming interface: FastEthernet0/0
  RPF nbr: FE80::C003:DFF:FE60:1

Embedded RP

FF7[scope]:0[RP Interface ID][Prefix Length in HEX]:[64 bit RP Prefix]:[32 bit group ID]

Whether only 64 (hex 40) is valid in [Prefix Length in HEX] portion ?

thanks !!

[Harold Ritter · Accepted solution]

The prefix length cannot be greater than 64 (hex 40).

If the RP address is 3000:1111::1, the corresponding embedded RP address could be:

FF75:120:3000:1111::1

or

FF75:130:3000:1111::1

or

FF75:140:3000:1111::1

Which will all work.

Regards,

[gongya001]

thanks so much for your patient explanation !!

[Harold Ritter]

You are very welcome!