Re: Using /31 for router links
Mark Smith <nanog@85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org> wrote:
What about NAT, ATM cell tax, unnecessary addressing fields in PTP protocols (including your beloved HDLC), SSAP, DSAP fields not being big enough in 802.2 necessitating SNAP, IPX directly over 802.3, AAL1 through AAL4, PPPoE "dumbell" MTUs and MSS hacks? Some of those are far worse sins in my opinion.
Hmm. PPPoE: this kludge is a direct fallout of abusing Ethernet for WAN/PTP. If all those xDSL users were willing to stick V.35 cards in their PCs and use "modems" that put out V.35 instead of Ethernet, the whole PPPoE kludge with all of its attendant MTU issues would have been completely unnecessary. Want PPP for authentication etc? Just run straight PPP (RFC 1662) over V.35 instead of Ethernet/PPPoE, HDLC has no fixed MTU unlike Ethernet (jogging my memory, all HDLC controllers which I recall working with allowed maximum frame size up to just a little under 2^16 octets or so), and one can thus have the standard MTU of 1500 octets on that PPP link! Oh, and yet another soapbox of mine, an xDSL modem that puts out V.35 instead of goddamn Ethernet would be a true modem: a modulator/demodulator that modulates/demodulates the bits at the electrical level without caring about what's in those bits. What everyone else in this fubared world calls an xDSL "modem" (a black box that puts Ethernet out) is not a modem at all (i.e., total misappropriation of the term), it is actually a bastardized router! These boxes forward packets between two network interfaces: the presented Ethernet interface and the internal (often horrendously non-standard and proprietary) HDLC or ATM interface on the actual line. A device that forwards packets between two different network interfaces is by definition a router, hence what everyone calls a "modem" is actually a bastardized router - bastardized because its routing (packet forwarding) function is something incomprehensible. The Ethernet-to-Ethernet NAT boxes that everyone else calls "routers" should be called "NATters" or something like that, anything but a router! A true router is a box with a few AUIs and a few V.35 ports sticking out of it, running some very capable, flexible and totally user-configurable packet forwarding software stack that supports all networking models: IP routing, MAC bridging, VC cross-connect. As for ATM... The part that totally baffles me about the use of ATM on xDSL lines is that I have never, ever, ever seen an xDSL line carrying more than one ATM VC. OK, there may be someone out there who has set up a configuration like that just for fun, but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38. So what then is the point of running ATM?!?! All the hyped benefits of ATM (a little cell can squeeze in the middle of a big packet without waiting for it to finish, yadda yadda yadda) are contingent upon having more than one VPI/VCI going across the interface! If every single non-idle cell going across that ATM interface is 0*35 or 0*38, the interface will never carry anything other a direct succession of cells making up an AAL5 packet, strictly in sequence and without interruption. So what's the point of ATM then? Why chop that packet up into cells only to transmit those cells in direct sequence one after another? Why not simply send that same packet in plain HDLC over the same copper pairs/fiber? OK, the backhaul network upstream of the DSLAM may be ATM and that one does have many VCs, so ATM *might* be of use there, but even in that case why not do FRF.8 in the DSLAM and keep the ATM strictly on the backhaul, sending HDLC down the copper pairs? <off the soapbox for the moment> MS
As for ATM... The part that totally baffles me about the use of ATM on xDSL lines is that I have never, ever, ever seen an xDSL line carrying more than one ATM VC. OK, there may be someone out there who has set up a configuration like that just for fun, but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38.
Multi-PVC is used (in the context of xSLAM<-->CPE), for example, for delivering IPTV+DSL. 0/35 and 0/38 are just arbitrary numbers, there are plenty of other random ones like 0/33 used by major service providers. Arguably your "99.999%" is way off.
[Michael Sokolov said:] *snip* but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38. So what then is the point of running ATM?!?! *snip* We've got several ADSL and SDSL circuits that carry two PVC's: 0/35 and 0/36. Covad has a product called "Voice Optimized Access". I won't go into the gory details of the underlying technology, but the second PVC is utilized for voice. Essentially two separate IP networks over one physical network, one with guaranteed bandwidth (by way of vbr-rt) and QoS through Covad's network. Sincerely, Bobby Glover Director of Information Services South Valley Internet -----Original Message----- From: msokolov@ivan.Harhan.ORG (Michael Sokolov) Date: Sat, 23 Jan 2010 18:52:51 To: <nanog@nanog.org> Subject: Re: Using /31 for router links Mark Smith <nanog@85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org> wrote:
What about NAT, ATM cell tax, unnecessary addressing fields in PTP protocols (including your beloved HDLC), SSAP, DSAP fields not being big enough in 802.2 necessitating SNAP, IPX directly over 802.3, AAL1 through AAL4, PPPoE "dumbell" MTUs and MSS hacks? Some of those are far worse sins in my opinion.
Hmm. PPPoE: this kludge is a direct fallout of abusing Ethernet for WAN/PTP. If all those xDSL users were willing to stick V.35 cards in their PCs and use "modems" that put out V.35 instead of Ethernet, the whole PPPoE kludge with all of its attendant MTU issues would have been completely unnecessary. Want PPP for authentication etc? Just run straight PPP (RFC 1662) over V.35 instead of Ethernet/PPPoE, HDLC has no fixed MTU unlike Ethernet (jogging my memory, all HDLC controllers which I recall working with allowed maximum frame size up to just a little under 2^16 octets or so), and one can thus have the standard MTU of 1500 octets on that PPP link! Oh, and yet another soapbox of mine, an xDSL modem that puts out V.35 instead of goddamn Ethernet would be a true modem: a modulator/demodulator that modulates/demodulates the bits at the electrical level without caring about what's in those bits. What everyone else in this fubared world calls an xDSL "modem" (a black box that puts Ethernet out) is not a modem at all (i.e., total misappropriation of the term), it is actually a bastardized router! These boxes forward packets between two network interfaces: the presented Ethernet interface and the internal (often horrendously non-standard and proprietary) HDLC or ATM interface on the actual line. A device that forwards packets between two different network interfaces is by definition a router, hence what everyone calls a "modem" is actually a bastardized router - bastardized because its routing (packet forwarding) function is something incomprehensible. The Ethernet-to-Ethernet NAT boxes that everyone else calls "routers" should be called "NATters" or something like that, anything but a router! A true router is a box with a few AUIs and a few V.35 ports sticking out of it, running some very capable, flexible and totally user-configurable packet forwarding software stack that supports all networking models: IP routing, MAC bridging, VC cross-connect. As for ATM... The part that totally baffles me about the use of ATM on xDSL lines is that I have never, ever, ever seen an xDSL line carrying more than one ATM VC. OK, there may be someone out there who has set up a configuration like that just for fun, but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38. So what then is the point of running ATM?!?! All the hyped benefits of ATM (a little cell can squeeze in the middle of a big packet without waiting for it to finish, yadda yadda yadda) are contingent upon having more than one VPI/VCI going across the interface! If every single non-idle cell going across that ATM interface is 0*35 or 0*38, the interface will never carry anything other a direct succession of cells making up an AAL5 packet, strictly in sequence and without interruption. So what's the point of ATM then? Why chop that packet up into cells only to transmit those cells in direct sequence one after another? Why not simply send that same packet in plain HDLC over the same copper pairs/fiber? OK, the backhaul network upstream of the DSLAM may be ATM and that one does have many VCs, so ATM *might* be of use there, but even in that case why not do FRF.8 in the DSLAM and keep the ATM strictly on the backhaul, sending HDLC down the copper pairs? <off the soapbox for the moment> MS
On 1/23/10 11:52 AM, Michael Sokolov wrote:
Oh, and yet another soapbox of mine, an xDSL modem that puts out V.35 instead of goddamn Ethernet would be a true modem: a modulator/demodulator that modulates/demodulates the bits at the electrical level without caring about what's in those bits.
Back in the days of Rhythms and Copper Mountain gear, Netopia had the D series routers which were actually xDSL to DSU units. Used to use them for customers who had T1 equipment (2500s, 2600s, 1600s, etc). Worked quite well. Though, I'm not sure they'd work these days, nor do I think they came in ADSL models either. -- Brielle Bruns The Summit Open Source Development Group http://www.sosdg.org / http://www.ahbl.org
On 23/01/10 19:52, Michael Sokolov wrote:
Mark Smith <nanog@85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org> wrote:
As for ATM... The part that totally baffles me about the use of ATM on xDSL lines is that I have never, ever, ever seen an xDSL line carrying more than one ATM VC. OK, there may be someone out there who has set up a configuration like that just for fun, but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38.
It's common practice down here in Italy to have more than one VC. One is used to carry data and the other one is used for VoIP, so that you don't have to do QoS on the data part. Ciao ! -- Massimiliano Stucchi BrianTel Srl stucchi@briantel.com Tel (+39) 039 9669921 | Fax (+39) 02 44417204 I-23807, Merate (Lecco), via Mameli 6 MS16801-RIPE
I agree! most of the xDSL providers all over the world follow the same standard of two VC's/ One for Data and One for voice. On Mon, Jan 25, 2010 at 7:20 AM, Massimiliano Stucchi <stucchi@briantel.com> wrote:
On 23/01/10 19:52, Michael Sokolov wrote:
Mark Smith <nanog@85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org> wrote:
As for ATM... The part that totally baffles me about the use of ATM on xDSL lines is that I have never, ever, ever seen an xDSL line carrying more than one ATM VC. OK, there may be someone out there who has set up a configuration like that just for fun, but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38.
It's common practice down here in Italy to have more than one VC. One is used to carry data and the other one is used for VoIP, so that you don't have to do QoS on the data part.
Ciao ! --
Massimiliano Stucchi BrianTel Srl stucchi@briantel.com Tel (+39) 039 9669921 | Fax (+39) 02 44417204 I-23807, Merate (Lecco), via Mameli 6 MS16801-RIPE
We use 5 PVCs for the IP video and one for Internet. Not as uncommon as you think. Frank -----Original Message----- From: Michael Sokolov [mailto:msokolov@ivan.Harhan.ORG] Sent: Saturday, January 23, 2010 12:53 PM To: nanog@nanog.org Subject: Re: Using /31 for router links Mark Smith <nanog@85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org> wrote:
What about NAT, ATM cell tax, unnecessary addressing fields in PTP protocols (including your beloved HDLC), SSAP, DSAP fields not being big enough in 802.2 necessitating SNAP, IPX directly over 802.3, AAL1 through AAL4, PPPoE "dumbell" MTUs and MSS hacks? Some of those are far worse sins in my opinion.
<snip> As for ATM... The part that totally baffles me about the use of ATM on xDSL lines is that I have never, ever, ever seen an xDSL line carrying more than one ATM VC. OK, there may be someone out there who has set up a configuration like that just for fun, but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38. So what then is the point of running ATM?!?! All the hyped benefits of ATM (a little cell can squeeze in the middle of a big packet without waiting for it to finish, yadda yadda yadda) are contingent upon having more than one VPI/VCI going across the interface! If every single non-idle cell going across that ATM interface is 0*35 or 0*38, the interface will never carry anything other a direct succession of cells making up an AAL5 packet, strictly in sequence and without interruption. So what's the point of ATM then? Why chop that packet up into cells only to transmit those cells in direct sequence one after another? Why not simply send that same packet in plain HDLC over the same copper pairs/fiber? OK, the backhaul network upstream of the DSLAM may be ATM and that one does have many VCs, so ATM *might* be of use there, but even in that case why not do FRF.8 in the DSLAM and keep the ATM strictly on the backhaul, sending HDLC down the copper pairs? <off the soapbox for the moment> MS
participants (7)
-
Brielle Bruns -
Erik L -
Frank Bulk -
Massimiliano Stucchi -
msokolov＠ivan.Harhan.ORG -
Ramanpreet Singh -
Robert Glover