IPv6 Summarization

I was working through IEWB Vol Lab 4 and ran across this summarization task for IPv6. I can do summarization when it comes to IPv4 but I was kind of sketchy on IPv6 summarization. Well I attempted the task and was close to say the least. So after I went through the whole task and got the details behind how it works, I thought why not post this here so others can benefit from it.

I am going to use IE’s addressing since I am working with it right now and I can show you guys the exact output from my routers.  Scenario is something like this:

 (— AREA 0——-)  (——————–AREA 1 —————–)  

BB2 ——- R1—(2001:141:1:12::/64)— R2 —(2001:141:1:25::/64)

What we are dealing with is that R2 has two different subnets, one on the FA0/0 and the other one on S0/0 towards R1. R1 has a connected out to BB2 and these routers are all running OSPFv3. The task asks as to summarize these two networks so that BB2 will receive one summary route. Rrom our understanding of OSPF, we know that OSPF routes can be summarized on two type of routers, ABRs and ASBRs. In this case we are dealing with an ABR (R1) so we will perform the summarization here. Let’s write down the two networks first:

2001:141:1:12::/64

2001:141:1:25::/64

Now let’s come up with a summary address that will include both networks. Now we can compare the two addresses and find out where the two addresses are different.

0012 and 0025

We all know that IPv6 address is 128bit (8 16-bit fields) so here we are dealing with the 4th 16-bit field. Now we have to change the two fields to binary but for that let’s do a quick review of HEX to binary conversion.

Hex fields range from 0 to 15:

0 through 9 and then 10 through 15 represented by A through F. Here is a quick breakdown of the binary representation of HEX:

So now let’s convert the HEX values to Binary:

0012 = 0000 0000 00 01 0010
0025 = 0000 0000 00 10 0101 

 Now we can convert the binary back to HEX and add this to our original IPv6 address.

0000 0000 0000 0000 = 0000 in HEX

Finally our summary address will look like this:

2001:141:1::/58

The reason we have a subnet mask of /58 is that the matching bits are now 6 bits less so 64-6=58.

Now let’s add this summary to R1.

R1(config)#ipv6 router ospf 1
R1(config-rtr)#area 1 range 2001:141:1::/58

Verify that the summary address is there:

R1#sh ipv6 route ospf
IPv6 Routing Table - 10 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
       U - Per-user Static route
       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
OE2  2001:51:51:51::/64 [110/20]
     via FE80::200:CFF:FE4E:479C, FastEthernet0/0
O   2001:141:1::/58 [110/0]
     via ::, Null0
O   2001:141:1:25::/64 [110/65]
     via FE80::20D:EDFF:FE26:1680, Serial0/0.1

Verify the OSPF Database

R1#sh ipv6 ospf database inter-area prefix

            OSPFv3 Router with ID (150.1.1.1) (Process ID 1)

                Inter Area Prefix Link States (Area 0)

  LS age: 151
  LS Type: Inter Area Prefix Links
  Link State ID: 3
  Advertising Router: 150.1.1.1
  LS Seq Number: 80000001
  Checksum: 0×7446
  Length: 36
  Metric: 65
  Prefix Address: 2001:141:1::
  Prefix Length: 58, Options: None

So here it is, this really helped me understand the summarization of IPv6 so I am hoping this would do the same for you. If there is anything you didn’t understand, feel free to contact me.