Re: Telnet over WAN latency troubleshooting

Rich Jordan wrote:
> so far no bottleneck has shown up in traceroutes, but again I can
> only run them (usefully) from the central site.

Doesn't generally matter. A traceroute measures the time for a packet to
make it TO a router and then BACK to you. So a bottleneck in either
direction will show up.


> The DSL router and
> DECserver don't provide statistics,

Try to get the DSL Router's full manuals. If there is a command line
interface, you may be able to get statistics out of the beast. What is
important is to look at the length of time since the DSL link was last
established, AND amount of time since the last PPPoE session was established.

Also, check to see if that router supports SYSLOG or SNMP so you could
capture events onto a computer.

> same level of packet loss though. We also tested large to make sure
> that the PPPoE underpinnings weren't causing large packet loss; that
> was the reason for reducing the firewall MTUs from 1500.

Because of the pesky PPPoE, you cannot use 1500. 1492 is the theoretical
limit because PPPoE uses 8 bytes of additional headers. However, some
ISPs reduce the MTU even more to increase efficiency of ATM packets
(which are multiple of 64 bytes).

But for Telnet, you wouldn't see a difference.

Once issue to look into which si quite obscure is to try to find out if
the box doing the PPPoE thing pads all packets to the MTU. Some low end
routers were designed to do that. So for every character you would send,
the router would send 1500 bytes over the DSL line. This would greatly
reduce your throughput. If your have a good ISP, they may be able to
trace some of your packets to see if they are padded or not.
.

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