Re: SMDS MTU
mogul (Jeffrey Mogul) Fri, 01 June 1990 17:38 UTC
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From: mogul (Jeffrey Mogul)
Message-Id: <9006011738.AA01057@acetes.pa.dec.com>
Date: 1 Jun 1990 1038-PDT (Friday)
To: kzm@nms.hls.com (Keith McCloghrie)
Cc: mtudwg
Subject: Re: SMDS MTU
In-Reply-To: kzm@nms.hls.com (Keith McCloghrie) / Thu, 31 May 90 23:15:05 PDT.
<9006010615.AA14764@nms.>
Don't know whether you saw this, but of interest is the SMDS MTU of 9188. Can we assume that by the time this is available, that all routers will have implemented the modified (for MTU-discovery) ICMP message which contains the MTU size. Else, it won't do much for the plateau algorithm. I noticed this too, but I don't think it's a serious problem, for several reasons: (1) The current table has a plateau at 8166 octets, which is something like 12% off from 9188 ... so the damage would be slight (remember, a 12% difference in packet size will cause much less than 12% difference in actual throughput). (2) Right now, there is only one MTU larger than 9188 that is known to me (the 16 Mbit Token ring's maximum possible MTU). That means that only in the case where someone connects such a LAN directly to an SMDS network will there be any issue at all. In all other cases, the SMDS MTU won't matter, because the sender's initial estimate will always be lower. [Does anyone know if anyone actually runs token rings with an MTU of 17914 octets?] (3) It's probably true that by the time anyone builds an IP router that supports SMDS, router vendors will know enough about MTU Discovery to judge whether they should implement it (i.e., it might not be a standard by then, but its destiny should be clear). -Jeff
- Re: SMDS MTU Jeffrey Mogul