icmp

[vinguy51]

hai....usually icmp (Internet Control message Protocol) is responsible for the traffic problems in the network....means if any collision happens on the network means it will send the messages to the source devices from where the packets was came from isn't it........here is there any relationship for icmp with router's queue management things.........give me brief explanation......if possible give me the related websites.........thanks in advanz.....

[Will.Spencer]

Let's think this through...

Weighted Fair Queueing, Class Based Weighted Fair Queueing, and Heirarchical Weighted Fair Queueing look at packet types, and therefore do not use ICMP.

Random Early Detection looks at congestion on the device level. RED just drops packets, which does not require ICMP.

Weighted Random Early Detection is like RED, but it also looks are the priority value in the IP header.

Traffic Shaping is much like RED, except the packets are queued instead of simply dropped.

Rate Limiting is a combination of WRED and Traffic Shaping. It looks at the priority value in the IP header and it queues packets instead of dropping them.

So, none of the QoS algorithms directly utilize ICMP. However, they do utilize IP, which may call ICMP automatically.

Next, let's tackle this problem from the opposite direction. Take a look at the complete list of ICMP messages:

• 0: Echo Reply
• 3: Destination Unreachable
• 4: Source Quench
• 5: Redirect
• 6: Alternate Host Address
• 8: Echo
• 9: Router Advertisement
• 10: Router Solicitation
• 11: Time Exceeded
• 12: Parameter Problem
• 13: Timestamp
• 14: Timestamp Reply
• 15: Information Request
• 16: Information Reply
• 17: Address Mask Request
• 18: Address Mask Reply
• 30: Traceroute

The only ICMP message which might be useful for QoS is 4: Source Quench.

However, Source Quench is discouraged for use by routers in RFC1812 and is really not used anymore. Microsoft Windows, for example, disregards it entirely.

[vinguy51]

hai.....actually SOURCE QUENCH message is to tell the source router that the destination router,s buffer is crossing the limit so stop on sending the packets .....isn't it .... here what is the exact limit ........100% buffer full or some 70% or 80% like....i want to know the exact one ....thanks in advanz.....

[Will.Spencer]

There is no standard limit, it is open to each implementer to determine what their hardware and software can handle.

Source Quench is defined in RFC 792: Internet Control Message Protocol:

A gateway may discard internet datagrams if it does not have the
buffer space needed to queue the datagrams for output to the next
network on the route to the destination network. If a gateway
discards a datagram, it may send a source quench message to the
internet source host of the datagram. A destination host may also
send a source quench message if datagrams arrive too fast to be
processed. The source quench message is a request to the host to
cut back the rate at which it is sending traffic to the internet
destination. The gateway may send a source quench message for
every message that it discards. On receipt of a source quench
message, the source host should cut back the rate at which it is
sending traffic to the specified destination until it no longer
receives source quench messages from the gateway. The source host
can then gradually increase the rate at which it sends traffic to
the destination until it again receives source quench messages.

The gateway or host may send the source quench message when it
approaches its capacity limit rather than waiting until the
capacity is exceeded. This means that the data datagram which
triggered the source quench message may be delivered.

And that's all of the "exact" that there is. :p