1. CSE4213 Computer Networks II
Supplementary Material
(VLSM and IPv6)
Course page:

2. Variable Length Subnet Mask
Let’s say there is a company with a Class C network /24.
Subnet 1 requires 10 hosts
Subnet 2 requires 10 hosts
Subnet 3 requires 10 hosts
Subnet 4 requires 10 hosts
Subnet 5 requires 50 hosts
Subnet 6 requires 100 hosts
How to subnet?

3. IPv6 Header Format

4. IPv6 Extension Header
The general form of an IPv6 datagram. Extension headers are optional -- the minimum datagram has a base header followed by data

5. Example
Two IPv6 datagrams in which (a) contains a base header plus data, and (b) contains a base header, route header, and data. The NEXT HEADER field in each header specifies the type of the item that follows.

6. IPv6 Options Extension Header
Because the size of the options header can vary from one datagram to another, the HEADER LEN field specifies the exact length.

7. IPv6 Fragmentation In IPv4 a router performs fragmentation
In IPv6 a sending host performs fragmentation. How?
A sending host sends a packet to the size of the first link. If a router along the path cannot handle, it will drop the packet and send ICMPv6 packet too big. The sending host then resend with smaller size.
Or simply send a minimum MTU size that all routers should support – 1280 bytes

8. IPv6 Fragmentation (2)

9. IPv6 Addressing

10. IPv4-Compatible IPv6 Addresses
For devices that speak both IPv4 and IPv6: dual stack

11. IPv4-Mapped IPv6 Addresses
Used for mapping IPv4 devices that are not compatible with IPv6 into the IPv6
address space; it begins with 80 zeroes followed by 16 ones. (only IPv4-capable)