Re: Questions about SRv6 mobile user-plane
Tom Herbert <[email protected]> Fri, 26 Jan 2018 18:27:16 -0800
| Newsgroups | gmane.ietf.mip6 |
|---|---|
| Message-ID | <CAPDqMepFiUPBNbidHokJYPMovGYRaxbtqHbuo-d4qXrjsh=jXw__25084.3278867707$1517019944$gmane$org@mail.gmail.com> |
--===============6036474945250973006== Content-Type: multipart/alternative; boundary="001a1146e1226ddff60563b8c0e2" --001a1146e1226ddff60563b8c0e2 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, Jan 26, 2018 at 5:35 PM, Sri Gundavelli (sgundave) < [email protected]> wrote: > Hi Tom, > > > I am working on a comparison between ILA and SRv6 for the mobile > user-plane. > > This is a good effort. I was wondering, about the key parameters that you > will use for this comparison between ILA/ILNP/LISP/HICN etc. For example, > ILA router the entries at the ILA router ( ID =E2=80=93 L OC - SIR Prefi= x), vs at > the LISP mapping system. How do you compare the two, a cache/MAP query > cost, vs a translation cost + local memory state for keeping that entry. > > Sri, https://tools.ietf.org/html/draft-herbert-ila-motivation-00 provides some comparisons between ILA and ILNP, encapsulations, SR, and transport layer mechanisms that can achieve some effects in mobility. The choice of mapping system is critical. The mapping of identifier, or equivalently virtual to physical address mapping, seems to be a common problem in mobility and networking virtualization. As you mentioned, LISP defines a query method to populate a mapping cache. I assume this problem needs to be tackled in SR for mobile user-plane but I'm not sure what solution is preferred after reading the draft. ILA partitions the problem into a two level hierarchy: ILA routers and IL forwarding nodes. This is somewhat analogous to core IP routers and nodes running neighbor discovery. ILA routers contain all the (possibly sharded) mappings. They are authoritative. Forwarding nodes are located close to user devices and maintain a working set cache of entries driven by user activity. If a packet doesn't hit the cache it's forwarded to a router that will do the ILA transformation. If the cache is hit, the packet can be transformed at the forwarding node to eliminate triangular routing. Caches can be populated by pull or push models. ILAMP (the ILA mapping protocol) supports both of these, but my current preference for scalability and mitigating DOS attacks on the cache is to use secure redirects sent by ILA routers (analogous to ICMP redirects). > On a different note, just curious if SID prefix can ever have topological > relevance and can be used for routing. In other words, can you ever route= a > packet without translating the SIR prefix of the destination address wit= h > the locator? Can SID prefix be used as a locator in some special cases? > Yes, the SIR prefix is routable to forward to an ILA router. This is necessary for the redirect mechanism I describe above. I suppose this could be contorted to make the SIR address be a home address like in MobileIP and locators are COAs (if my use of MobileIP terminology is correct). There also might be nodes in the network, as well as external nodes that don't do go through a cache to their packets need to hit an ILA router to get forwarded to the location of mobile nodes. An upshot of that is that edge routers might need to perform transformations (SIR to ILA) at high rates so the mechanism needs to be very efficient and amenable to HW implementation. Tom > Sri > > > > > > From: dmm <[email protected]> on behalf of Tom Herbert < > [email protected]> > Date: Friday, January 26, 2018 at 9:13 AM > To: "[email protected]" <[email protected]>, "[email protected]" <[email protected]> > Subject: [DMM] Questions about SRv6 mobile user-plane > > Hello, > > I am working on a comparison between ILA and SRv6 for the mobile > user-plane. I have some questions/comments about SRv6 and particularly on > the example use cases that were depicted in the slides that were presente= d > in IETF100: > > https://datatracker.ietf.org/meeting/100/materials/slides- > 100-dmm-srv6-for-mobile-user-plane/ > > - It's clear from the depicted use cases that extension header insertion > is being done by intermediate nodes, but extension header insertion is > currently prohibited by RFC8200. There was an I-D posted on 6man to allow > this for SR, but that was met with pushback. Is there going to be followu= p > to resolve this? > > - For the uplink use cases, this seems to be more like using SR to source > route to an egress router. In other words, it's not strictly related to > mobility. Is there some connection to mobility that I'm missing? > > - The size or number of SR headers in the uplink cases seems to be larger > than necessary (IMO minimizing these is important since each additional s= id > is ~1% overhead of standard MTU). In this first scenario sid[1]=3DA2::1 a= nd > DA=3DA2::1-- this seems to be redundant information. Also this depicts a > second SR being inserted, but the first one should no longer be relevant. > Why not just discard the first one and save the overhead? In the second > scenario, DA is changing from A2::1 to A3::1 > <https://maps.google.com/?q=3DA3::1&entry=3Dgmail&source=3Dg>, but AFAICT= that > was not done per the SR processing. What is the operation that happened > here? (it's actaully looks like an ILA transfomation). > > - Considering the points above, could this have been done in the followin= g > manner to minimize overhead? A1 creates one SRH with one sid and makes > DA=3DA2. A2 makes DA=3DA3. At A3 SR is processed, DA is restored to Inter= net > address, and EH is removed. > > - For downlink this does see to be relevant to mobility. But I have the > same question, wouldn't it be less overhead to only use one SRH and one > sid? i.e. A3 creates an SRH with just one sid that is the S:: (identifier > in identifier/locator speak) and set DA to A2, and then A2 sets DA to A1, > A1 restores original packet for delivery. > > - One possible typo. In the last use case slide SA=3DS:: and DA=3DD::, I > believe these should be swapped? > > Thanks, > Tom > > > > > --001a1146e1226ddff60563b8c0e2 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><br><div class=3D"gmail_extra"><br><div class=3D"gmail_quo= te">On Fri, Jan 26, 2018 at 5:35 PM, Sri Gundavelli (sgundave) <span dir=3D= "ltr"><<a href=3D"mailto:[email protected]" target=3D"_blank">sgundave@= cisco.com</a>></span> wrote:<br><blockquote class=3D"gmail_quote" style= =3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding= -left:1ex"> <div style=3D"word-wrap:break-word;color:rgb(0,0,0);font-size:14px;font-fam= ily:Calibri,sans-serif"> <div>Hi Tom,</div><span class=3D"gmail-"> <div><br> </div> <div>> I am working on a comparison between ILA and SRv6 for the mobile = user-plane.</div> <div><br> </div> </span><div>This is a good effort. I was wondering, about the key parameter= s that you will use for this comparison between ILA/ILNP/LISP/HICN etc. For= example, ILA router the entries at the ILA router ( ID =E2=80=93 L OC =C2= =A0- SIR Prefix), vs at the LISP mapping system. How do you compare the two, a cache/MAP query cost, vs a translation cost + lo= cal memory state for keeping that entry.=C2=A0</div> <div><br></div></div></blockquote><div>Sri,</div><div><br></div><div><a hre= f=3D"https://tools.ietf.org/html/draft-herbert-ila-motivation-00">https://t= ools.ietf.org/html/draft-herbert-ila-motivation-00</a> provides some compar= isons between ILA and ILNP, encapsulations, SR, and transport layer mechani= sms that can achieve some effects in mobility.<br></div><div><br></div><div= >The choice of mapping system is critical. The mapping of identifier, or eq= uivalently virtual to physical address mapping, seems to be a common proble= m in mobility and networking virtualization. As you mentioned, LISP defines= a query method to populate a mapping cache. I assume this problem needs to= be tackled in SR for mobile user-plane but I'm not sure what solution = is preferred after reading the draft.</div><div><br></div><div>ILA partitio= ns the problem into a two level hierarchy: ILA routers and IL forwarding no= des. This is somewhat analogous to core IP routers and nodes running neighb= or discovery.=C2=A0 ILA routers contain all the (possibly sharded) mappings= . They are authoritative. Forwarding nodes are located close to user device= s and maintain a working set=C2=A0 cache of entries driven by user activity= . If a packet doesn't hit the cache it's forwarded to a router that= will do the ILA transformation. If the cache is hit, the packet can be tra= nsformed at the forwarding node to eliminate triangular routing. Caches can= be populated by pull or push models. ILAMP (the ILA mapping protocol) supp= orts both of these, but my current preference for scalability and mitigatin= g DOS attacks on the cache is to use secure redirects sent by ILA routers= =C2=A0 (analogous to ICMP redirects).</div><div>=C2=A0</div><blockquote cla= ss=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid = rgb(204,204,204);padding-left:1ex"><div style=3D"word-wrap:break-word;color= :rgb(0,0,0);font-size:14px;font-family:Calibri,sans-serif"><div> </div> <div>On a different note, just curious if SID prefix can ever have topologi= cal relevance and can be used for routing. In other words, can you ever rou= te a packet without translating =C2=A0the SIR prefix of the destination add= ress with the locator? Can SID prefix be used as a locator in some special cases?</div></div></blockquote><div><= br></div><div>Yes, the SIR prefix is routable to forward to an ILA router. = This is necessary for the redirect mechanism I describe above. I suppose th= is could be contorted to make the SIR address be a home address like in Mob= ileIP and locators are COAs (if my use of MobileIP terminology is correct).= There also might be nodes in the network, as well as external nodes that d= on't do go through a cache to their packets need to hit an ILA router t= o get forwarded to the location of mobile nodes. An upshot of that is that = edge routers might need to perform transformations (SIR to ILA) at high rat= es so the mechanism needs to be very efficient and amenable to HW implement= ation.</div><div><br></div><div>Tom</div><div><br></div><blockquote class= =3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rg= b(204,204,204);padding-left:1ex"><div style=3D"word-wrap:break-word;color:r= gb(0,0,0);font-size:14px;font-family:Calibri,sans-serif"> <div><br> </div> <div>Sri</div> <div><br> </div> <div><br> </div> <div><br> </div> <div><br> </div> <div><br> </div> <span id=3D"gmail-m_5381827898059836675OLK_SRC_BODY_SECTION"> <div style=3D"font-family:Calibri;font-size:11pt;text-align:left;color:blac= k;border-width:1pt medium medium;border-style:solid none none;border-bottom= -color:initial;border-left-color:initial;padding:3pt 0in 0in;border-top-col= or:rgb(181,196,223);border-right-color:initial"><span class=3D"gmail-"> <span style=3D"font-weight:bold">From: </span>dmm <<a href=3D"mailto:dmm= [email protected]" target=3D"_blank">[email protected]</a>> on behalf= of Tom Herbert <<a href=3D"mailto:[email protected]" target=3D"_blank"= >[email protected]</a>><br> <span style=3D"font-weight:bold">Date: </span>Friday, January 26, 2018 at 9= :13 AM<br> <span style=3D"font-weight:bold">To: </span>"<a href=3D"mailto:dmm@iet= f.org" target=3D"_blank">[email protected]</a>" <<a href=3D"mailto:dmm@i= etf.org" target=3D"_blank">[email protected]</a>>, "<a href=3D"mailto:il= [email protected]" target=3D"_blank">[email protected]</a>" <<a href=3D"mailto:= [email protected]" target=3D"_blank">[email protected]</a>><br> </span><span style=3D"font-weight:bold">Subject: </span>[DMM] Questions abo= ut SRv6 mobile user-plane<br> </div><div><div class=3D"gmail-h5"> <div><br> </div> <div> <div> <div dir=3D"ltr"> <div>Hello,</div> <div><br> </div> <div>I am working on a comparison between ILA and SRv6 for the mobile user-= plane. I have some questions/comments about SRv6 and particularly on the ex= ample use cases that were depicted in the slides that were presented in IET= F100:</div> <div><br> </div> <a href=3D"https://datatracker.ietf.org/meeting/100/materials/slides-100-dm= m-srv6-for-mobile-user-plane/" target=3D"_blank">https://datatracker.ietf.o= rg/<wbr>meeting/100/materials/slides-<wbr>100-dmm-srv6-for-mobile-user-<wbr= >plane/</a><br> <div><br> </div> <div>- It's clear from the depicted use cases that extension header ins= ertion is being done by intermediate nodes, but extension header insertion = is currently prohibited by RFC8200. There was an I-D posted on 6man to allo= w this for SR, but that was met with pushback. Is there going to be followup to resolve this?</div> <div><br> </div> <div>- For the uplink use cases, this seems to be more like using SR to sou= rce route to an egress router. In other words, it's not strictly relate= d to mobility. Is there some connection to mobility that I'm missing?</= div> <div><br> </div> <div>- The size or number of SR headers in the uplink cases seems to be lar= ger than necessary (IMO minimizing these is important since each additional= sid is ~1% overhead of standard MTU). In this first scenario sid[1]=3DA2::= 1 and DA=3DA2::1-- this seems to be redundant information. Also this depicts a second SR being inserted, but t= he first one should no longer be relevant. Why not just discard the first o= ne and save the overhead? In the second scenario, DA is changing from A2::1= to <a href=3D"https://maps.google.com/?q=3DA3::1&entry=3Dgmail&sou= rce=3Dg">A3::1</a>, but AFAICT that was not done per the SR processing. What is the operation that happened here? (it&= #39;s actaully looks like an ILA transfomation).</div> <div><br> </div> <div>- Considering the points above, could this have been done in the follo= wing manner to minimize overhead? A1 creates one SRH with one sid and makes= DA=3DA2. A2 makes DA=3DA3. At A3 SR is processed, DA is restored to Intern= et address, and EH is removed.</div> <div><br> </div> <div>- For downlink this does see to be relevant to mobility. But I have th= e same question, wouldn't it be less overhead to only use one SRH and o= ne sid? i.e. A3 creates an SRH with just one sid that is the S:: (identifie= r in identifier/locator speak) and set DA to A2, and then A2 sets DA to A1, A1 restores original packet for deliv= ery.</div> <div><br> </div> <div>- One possible typo. In the last use case slide SA=3DS:: and DA=3DD::,= I believe these should be swapped?</div> <div><br> </div> <div>Thanks,</div> <div>Tom</div> <div><br> </div> <div>=C2=A0</div> <div><br> </div> <div><br> </div> </div> </div> </div> </div></div></span> </div> </blockquote></div><br></div></div> --001a1146e1226ddff60563b8c0e2-- --===============6036474945250973006== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ dmm mailing list [email protected] https://www.ietf.org/mailman/listinfo/dmm --===============6036474945250973006==--