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12 messages in net.nether.puck.cisco-nsp[c-nsp] MTU Question on T1| From | Sent On | Attachments |
|---|---|---|
| Richard J. Sears | Jan 24, 2005 12:33 pm | |
| Gert Doering | Jan 24, 2005 12:54 pm | |
| Richard J. Sears | Jan 24, 2005 1:13 pm | |
| Gert Doering | Jan 24, 2005 1:28 pm | |
| Joe Maimon | Jan 24, 2005 1:28 pm | |
| Jon Lewis | Jan 24, 2005 1:39 pm | |
| Rodney Dunn | Jan 24, 2005 2:39 pm | |
| Bill Wichers | Jan 24, 2005 7:46 pm | |
| Richard J. Sears | Jan 24, 2005 8:15 pm | |
| Jon Lewis | Jan 24, 2005 8:18 pm | |
| Jay Hennigan | Jan 24, 2005 8:27 pm | |
| Gert Doering | Jan 25, 2005 3:08 am |
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| Subject: | [c-nsp] MTU Question on T1 | Actions... |
|---|---|---|
| From: | Richard J. Sears (rse...@americanIS.net) | |
| Date: | Jan 24, 2005 8:15:27 pm | |
| List: | net.nether.puck.cisco-nsp | |
Hi Bill -
I am sure that they are messing it up, but they have not identified that error as of yet, even with me explaining it to them.
All they say if to do a 40000 byte packet ping from a windows box to another windows box across the T1 and until that comes back below 50ms, don't bother them!!
On Mon, 24 Jan 2005 19:47:08 -0500 (EST) "Bill Wichers" <billw at waveform.net> wrote:
Right now the equipment is not working as advertised. According to the vendor, this is because a ping of 40000 bytes is returning a rtt of 400ms across the dual T1s.
Are you sure the vendor doesn't mean kilo-BIT? As others have said, a T1 can only move about 190 or so kB/sec, so even with "ideal" performance, an mpp bundle with two T1s can only move 40 kB to one end and back in about 210 ms (on a very short link too). IMHO, intracity T1 links are usually in the 4-8 ms range for RTT (with an IP ping), and thats with a 7576 w/ RSP4 on one end (our aggregation router), and any little cisco on the CPE end. Intercity links will have longer RTTs due to the increased distances involved. These are all physical limits and have nothing to do with MTU or anything you may have configured on either end of your link.
BTW, with a 40 kb (kilo-BIT) ping, you'll see more around 21-30 ms RTT. That's about a 5 kB packet. I'm thinking your vendor may be messing up the old convention of capital 'B' meaning 'bytes', and lower-case 'b' meaning 'bits'.
Their entire claim is that because they cannot ping the other router with a 40000 byte packet with less than 50ms latency, that is the entire problem and until we fix that issue - don't call them back.
So - my brain begins to think and I go to my 7500s, ping any number of customers with T1s with no traffic on them with Cisco's max packet size of 18024 - I see around 225ms.
Your brain thunk correctly :-) Call back your vendor and play the part of the BOFH and inform them that they do not know what they are talking about network-wise, and that they need to fix their software.
-Bill
***************************** Waveform Technology UNIX Systems Administrator
****************************************** Richard J. Sears Vice President American Internet Services
---------------------------------------------------- rsears at adnc.com http://www.adnc.com
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