Routing and packet-primacies

[seantech]

Is a network standard that defines certain network packets having some primacy or state of urgency over another packet, what in turn would possibly have a router handle that one 'more important' packet first?

 

Fictitious Problem:

 

Let's say that I would have a mission-critical packet containing data that engages an emergency override/stop function on a piece of machinery. The goal would be to have emergency-stop buttons connected to one or more machines over a real busy ethernet cable (that is used for a broad number of other applications) without sacrificing any or all response time. Every second does after all count!

 

Could I in such a situation preferably use an ICMP packet because it is more 'important' than a standard data-packet, or is there no such thing in router-land?

[paul]

What you're talking abot is ToS (Type of Service) and QoS (Quality of service)

 

if you are using ICMP packets, you can setup a router to prioritize (spelling :) ) the ICMP packet.

This is a common trick for ssh connections to servers.

If the packet is undefinable and you cannot use ToS, the you could invest in a couple of VLAN 802.1q routers that will do Port based QoS

imagine a 4 port router at each end of a link. You can define port 1 in both routers gets a higher priority than any other port.

This is a common trick in VOIP design, giving priority to Voice traffic on a port, since VOIP can change its packets (or has a number of different packet types) and they can't be easily defined in ToS.

 

All this depends on what hardware you buy. They all do it from a cheap entry level dlink, to a flash watchguard/cisco/allied telesyn/name your brand

[seantech]

What you're talking abot is ToS (Type of Service) and QoS (Quality of service)

 

if you are using ICMP packets, you can setup a router to prioritize (spelling :) ) the ICMP packet.

 

You have to manually prioritize the packet-type though, right? It's not a case of it being in some tcp/ip standard that has been included in a premium-brand routers' tcp/ip stack that can be utilized by swiching an extra bit in your ip-header?

 

 

If the packet is undefinable and you cannot use ToS, the you could invest in a couple of VLAN 802.1q routers that will do Port based QoS.

 

Won't that rely on the network-priority of the VLAN that has been set up? VLAN uses (I thought three) bits for setting priority. You wouldn't by chance know if it would be possible to 'melt' that into, say, ICMP packets / mask a VLAN packet like ICMP for a router, perhaps still keeping the rest of it's functionality intact?

[paul]

With ToS, the way I understand it, is that you define 1 or 2 parts of the packet.

In the case of ssh this would be tcp, and port 22. in the case of ping it would be just 1 part .. ICMP

If the packet scheduler sees tcp on port 22 it gives it higher priority.

You manually define a minimum bandwidth with ToS, but it is burstable. if the network is quiet it will use more bandwidth. Like wise if the ToS (in this case ssh) is quiet, the defined minimum bandwidth will be used by the other network comms, until the packet scheduler sees tcp on port 22

 

With VLANs there are a bunch of ways to schedule packets. The easiest is to use "port" based vlan'ing. By "port" based, I mean physical ports on a router .. Network Interface Cards etc .. This, of course, requires physical segregation of your high priority network

net 1-                                                - net 1
       |                                               |
       |--{router}-------------{router}---|
       |                                               |
net 2-                                                - net 2

I've done this with some micronet routers, and it works well

 

You can also "tag" packets for scheduling. Where a vlan router will tag packets that you have defined. I've not done this .. but it can be done

 

What I have done is a combo of ToS and iptables, using fwmark. My interegation was again port based (network port, Not Physical port)

I using the prerouting table in iptables to mark packets. Using fwmark you can mark the packets on port 22, then use ToS to prioritize anything with a mark of xxxx

I marked packets on port 22 with a mark 4, then I can use ToS to look for packets with a header "mark" of 0x004

This method introduces some interest options.

Iptables looks at the entire packet header, so you can mark based on srcip or destip

example:

packet from ip x.x.x.x mark 4

now you can up (or down) thwe priority of all traffic coming from x.x.x.x

 

thoughts?