My customer has the need to run MPPP over disparate
networks each one have different bandwidths and latencies. One is a CSU/FT1, one is a dedicated four wire modem and the third is a satellite
shot. Does it take any special fine tuning to make up for these differences?
Yeah, the fine-tuning that you need is not to do it.
First of all, MPPP works very poorly in practice if the constituent links are very different, and from your current setup, looks like all 3 links are going to different routers, requiring something like MLPPP to stitch them together, which implies even worse performance. The overhead and processor-load required to properly stitch together data over the 3 links you propose, especially the satellite link, are almost certainly going to exceed whatever benefit there will be.
But still, this is their requirement. They want to aggregate the bandwidth from all 3 of these links. I've tried to talk them into a layer 3 solution, but no go. The only thing I could come up with was Multilink PPP
Xavier is right, MPPP is not the solution.
If load balancing is the requirement, try accomplishing this at Layer 3, rather than Layer 2.
You can't use Multilink PPP over three such different bandwidth links, especially satellite link. One of our satellite links has min. of 650ms latency (on a good day), most of time is around 750ms latency. You could use multiple default routes for all three links, if you want to do load balance (all though is hard to do in this case), you could disable the route cache. I would leave the route cache on and just do three default routes. Also, for whats worth, our satellite link experience many short downtimes because of sun interference, specially this year. The downtime normally last about 5 to 15 min.
"this is their requirement"
You, as someone who supposedly has networking knowledge then should be confident enough to talk them out of it.
If you were is a criminal defense lawyer, and your client was caught on video commiting a crime, his "REQUIREMENT" may be to fight the case, but you knowing he will lose, don't want to see him get 4 times as much jail time, should convince him to plea guilty.
MLPPP wont work. It will freeze your flows and cause chaos to your routers CPU. Does this Client also
have the "Requirement" of running BGP will full tables on a 2500 ?
On my next job, it is "my requirement" that I get paid a billion dollars for doing nothing.
Exactly, sometimes you have to stand up to the
client and tell them what's up. If it's not feasible, it's not feasible. You're a network engineer, not a miracle worker.
This is the Military, there a lot of issues and reasons why they have to do it this way, way to many to go into here. Trust me when I say that they are 100% convinced that they need this bandwidth for this application, and at this site these are their ONLY options! I told them up-front this would not work, and listed all of the same reasons list here, but they are still going to do this. BTW, WHY will MLPPP frezze the flows?
MLPPP working at layer 2 dosen't care about layer 3 and higher things. I once ran MLPPP on two T-1 lines, and the difference in speed on them made my
telnet feel like i was waiting for someone to type the responses (the ones ios sends automatically)
MLPPP will weigh thresholds like link saturation, etc, but if it takes 20ms to go over t-1, and 600ms to go over satellite, TCP will have major issues when re-ordering packets. Think of its as your destination getting packets 1,2, 7,9 while waiting
a while for 3,4,5,6. MLPPP will do exactly that. I used a sniffer to see these things. TCP dosent like
this and will suffer. It is basically MLPPP makes your connection only as responsive as your slowest (most latent) link. Satellite is miserable with TCP.
Maybe your using UDP or something that can handle this better.. but I still would not risk it. Just get all equal links, preferably with the same carrier to the same carriers route. then it works best.
Actually, that is not true. You can in theory use MPPP over 3 different bandwidth links. It's just a bad idea. But you could do it if you really really want to.