Date: Sat, 24 Nov 2001 15:27:19 -0800 From: "Kevin Oberman" <oberman@es.net> To: puga@mauibuilt.com Cc: Dru <genisis@istar.ca>, freebsd-questions@FreeBSD.ORG Subject: Re: IPFW/VLAN Message-ID: <200111242327.fAONRJd00822@ptavv.es.net> In-Reply-To: Your message of "Sat, 24 Nov 2001 13:00:22 -1000." <3C002685.AE3A0D1@mauibuilt.com>
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> Date: Sat, 24 Nov 2001 13:00:22 -1000 > From: Richard Puga <puga@mauibuilt.com> > Sender: owner-freebsd-questions@FreeBSD.ORG > > Yes I do have the vlan entry in my kernel. I have tried it with and without. > > The MTU of the fxp cards it set to its new default of 1500 (as of 4.4) and > curiously enough > can not be set higher as the maximum length of an ether net packet is 1518. > > The bridge passes the 802.1q packets just fine and I can view them with > tcpdump. > > it seems that ipfw ignores them, either treating them as a malformed ether > net packet or one that > is not ip.. im not sure that's just a guess.. MTU != Frame size...MTU == Packet size The MTU is a specification of the largest IP packet that may be transmitted over an interface. The MTU does not include the Ethernet framing (6 bytes destination + 6 bytes source + 2 bytes protocol + 4 bytes FCS). Nor does it include any bytes used for an 802.1q VLAN tag. Because some older Ethernet hardware cannot handle the new, extended frame size to allow for 802.1q, you are stuck with reducing the MTU. R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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