smart@manta.mel.dit.csiro.au (Bob Smart) (08/20/90)
I am interested in the possibility of using terrestrial low-bandwidth links for interactive traffic and satellite links for file transfers and other applications that don't have real-time expectations (including large 24 colour bit map images which would clog the interactive pipe). So I would like to be able to set the cisco up to route packets for the same destination networks to one of two different interfaces depending on TOS field and also on the size of the packet. The latter is more relevant at the moment since few applications (if any) set the TOS field. Can you do this with a Cisco? I can't see how from the manual. Does Cisco plan to have this capability? Should I be looking at some other product? I remember reading that it has been done. Bob Smart <smart@mel.dit.csiro.au>
forster@cisco.com (Jim Forster) (08/20/90)
Bob, Sorry, we don't support TOS routing. 4.4BSD is rumored to have such capability, but I don't know of anyone that has it now. In 8.2 we do support TOS queueing. After routing, the packet is placed on one of 4 output queues. The factors that influence which queue can include protocol, and whether the packet matches an access list. So you can make Bridged LAT & Telnet higher priority than FTP, for instance. We don't use packet size in deciding which queue to use. How do you think packet size should be used? Jim Forster cisco Systems
gfw@pueblo.att.com (08/21/90)
> Date: Sun, 19 Aug 90 23:10:54 PDT > From: Jim Forster <forster@cisco.com> > > Bob, > > Sorry, we don't support TOS routing. 4.4BSD is rumored to have such > capability, but I don't know of anyone that has it now. > > In 8.2 we do support TOS queueing. After routing, the packet is placed on > one of 4 output queues. The factors that influence which queue can include > protocol, and whether the packet matches an access list. So you can make > Bridged LAT & Telnet higher priority than FTP, for instance. We don't > use packet size in deciding which queue to use. How do you think packet size > should be used? While the capability described above is a step in the right direction, I would prefer to be able to configure my routers so that any packet with length <= N is queued before any packet > N. This way all character echo traffic (and other short packets) get sent out before longer file transfer traffic. I would hope that I could pick N (e.g., in case I had telnet/rlogin and not xterm, or vice versa). If I understand the queueing in 8.2, keyed on access list, I would have to set up an access list for each application protocol I wanted to flag for special queueing. This means that the router has to delve into the headers to look at every packet (slowing things down?) and that I have to identify all the application ports (telnet, rlogin, xterm, in-house applications, etc.) that I might like to give higher priority. This type of queueing is particularly important with slower speed serial lines (less than full T1) that already have long serialization and propagation times (e.g., international links). Of course, support for real TOS would be nice (but then we'd also have to hammer on our host software providers to specify TOS in the packets the applications send--and we know how responsive they are ;-). Greg Wetzel (708) 979-4782 G_F_Wetzel@att.com AT&T Bell Laboratories (IH 1B-213) 2000 N. Naperville Road Naperville, IL 60566