Internet Control Message Protocol for IPv6(ICMPv6) compared to ICMPv4 has multiple purposes with additional messages for reporting the source nodes about the packet delivery.
The ICMPv6 header contains the type, code, checksum and data(usually not used) part.
The ICMPv6 messages provide various functionalities to IPv6 protocol that includes,
Path MTU discovery:
The IPV6 packet is not fragmented in the intermediate routers, the fragmentation can happen in the source itself, to have a seamless IPv6 packet transfer without fragmentation we need to find the size of the MTU bottleneck and send packets with minimum MTU.
IPv6 uses ICMPv6 type 2(packet too big) for its operation. Let us consider the client(X) needs to communicate with the server(Y) where there are 3 routers Ra, Rb, Rc to hop.
X ---------Ra---------Rb---------Rc---------- Y
Usually the packet from the client(X) is sent with a MTU of 1500bytes, if Ra has MTU of 1400 bytes, it sends back ICMPv6 message with type2 to inform the packet is too big and use the MTU of 1400. Above said is continued till Rc and then the PMTU discovery is successful.
If the network is small size, it is advisable to use the same MTU size on all the router to avoid the IPv6 packet using the minimum MTU size and the time involved in this discovery could be avoided.
The ICMPv6 header contains the type, code, checksum and data(usually not used) part.
The ICMPv6 messages provide various functionalities to IPv6 protocol that includes,
- Replacement of ARP
- Stateless Autoconfiguration
- Duplicate Address Detection(DAD)
- Path MTU Discovery
- Prefix Renumbering
Path MTU discovery:
The IPV6 packet is not fragmented in the intermediate routers, the fragmentation can happen in the source itself, to have a seamless IPv6 packet transfer without fragmentation we need to find the size of the MTU bottleneck and send packets with minimum MTU.
IPv6 uses ICMPv6 type 2(packet too big) for its operation. Let us consider the client(X) needs to communicate with the server(Y) where there are 3 routers Ra, Rb, Rc to hop.
X ---------Ra---------Rb---------Rc---------- Y
Usually the packet from the client(X) is sent with a MTU of 1500bytes, if Ra has MTU of 1400 bytes, it sends back ICMPv6 message with type2 to inform the packet is too big and use the MTU of 1400. Above said is continued till Rc and then the PMTU discovery is successful.
If the network is small size, it is advisable to use the same MTU size on all the router to avoid the IPv6 packet using the minimum MTU size and the time involved in this discovery could be avoided.
"Cisco Self-Study: Implementing Cisco IPv6 Networks (IPV6)" This book is highly useful in understanding the concepts, I would recommend this for the people who already have basic knowledge about IPV6.
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