Unit 5, Assignment 1
IT283 Networking with TCP/IP
Part 1
| Message Type | Description |
| Router Solicitation | A host on the network comes online and requests information from a router regarding its address. Done immediately instead of waiting for next cycle. |
| Router Advertisement | Answering message from router to a new host about its link layer address. Also sent out at intervals to hosts connected to update tables with information about routing, packet size and format. |
| Neighbor Solicitation | A message sent from one node on a network to another to verify the link-layer address of itself or the other node, checking to see that they do not have the same address. |
| Neighbor Advertisement | Message sent from a node in reply to the solicitation, or if a change occurs in itself, to other nodes indicating information about its address. This helps in determining adjacency. |
| Redirect | Message from router to sender indicating a better route for traffic to go to reach destination. |
| Process | Description |
| Address Resolution | How the host figures out who its neighbors are via the Neighbor Solicitation and Advertisement messages. |
| Neighbor Unreachability Detection | How the host determines if a previously connected neighbor is still available for connection. |
| Duplicate Address Detection | How the host determines if the IPv6 address assigned to it is currently in use by another host and requesting a new one if it is. |
| Router Discovery | Nodes configuring their default gateways after sending router solicitation messages to other routers on the network, and configuring other information based on the responses. |
| Redirect Function | Used by routers to indicate to hosts that a different hop should be used to route traffic to a specific destination more efficiently. This router forwards packet to next hop on its way to the destination. |
Part II
- Five ICMPv6 Message types for Neighbor Discovery
- Comparing RS to RA, and NS to NA
- Router Solicitation messages and Router Advertisement messages are messages that hosts use to figure out who they are and how to send data on a specific network. This process is done somewhat automatically. Router Solicitation messages are used for finding out if there are routers on the network which use IPv6, and if so they request information about the network itself for address configuration purposes. These messages may be sent as soon as a host becomes active. Router Advertisement messages are messages broadcast to hosts on the network from routers at certain intervals, or in response to a Router Solicitation message from a specific host. These messages contain information about the link prefixes, the MTU of the link, and other options (Carrell, 2012).
- Neighbor Solicitation and Advertisement messages are meant to be sent between different hosts on the network itself. Neighbor Solicitation messages are sent out from one host to another on the network for a few different reasons. Typically, it is just trying to see if the other host is still available for receiving traffic. Other uses for this message type are to determine if its link-layer address is already being used on the network by another host. Neighbor Advertisement messages are sent in response to the solicitation like the router advertisement message. The main function of this message is to let the hosts know the addresses of their neighbors to build up a table.
- Conceptual Host Model, RFC 4861
- The conceptual host model outlined in RFC 4861 describes several pieces of data for each host will organize its data for interacting with another host. The document is only concerned with the neighbor discovery process. The hosts on the network are required (under this model) to maintain several different pieces of data. Neighbor Cache – A table of neighbors recently accessed by the host which has data about the link-layer address, information about unsent packets, and what to do if the unreachability detection protocol is engaged. Destination Cache – a table of destinations the host has sent information to recently; shall include items like IP addresses for the next hop to the destination, uses information updated by redirect messages, may also include PMTU. Prefix List – a table of prefixes which show the on-link addresses; this list is generated from router advertisement messages and contains an invalidation timer which is used to indicate when a new message is needed. Default Router List – a list of routers through which information can be sent, these are entries in the Neighbor Cache. Sending data is prioritized by known-good connections, over those with shaky ones. These also carry an invalidation timer to let the host know when to reach out to the router again .
- Neighbor Discovery Process
ICMPv6 Redirect Frames:
Frame 675: Current Hop Limit – 64. MTU – 1500. Maximum Transmission Unit.
Frame 3: Duplicate Address Detection is a process by which a node checks the IPv6 address it wants to use against other nodes on the network using Neighbor Advertisement messages.
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