I think you'll find that that's not really the case.
/30's are still quite the rage in the service provider world,
though ip un-number works well enough for the customer attach
access-router application.
Too bad Cisco can't embrace the /31. 8-)
George
> From: "Barry Raveendran Greene" <bgreene@cisco.com>
> To: "Vinod Anthony Joseph Cherunni" <vac@antarix.net>
> Cc: <cisco-nsp@puck.nether.net>
> Subject: RE: [nsp] BGP Advertisements
> Date: Sat, 3 Feb 2001 08:18:15 -0800
>
> Hello Vinod,
>
> Why are you using /30s that take up address space and increase the size of
> your IGP? Use IP Unnumbered. IP Unnumbered is the BCP of running an Internet
> operations.
>
> As to your question below, use the following as references:
>
> ISP Essentials Power Session
> http://www.cisco.com/public/cons/isp/documents/IOSEssentials_Seminar.zip
>
> BGP Routing Workshop
> http://www.cisco.com/public/cons/workshops/bgp/
>
> In the BGP Routing Workshop, look specifically for the BCP (Best Common
> Practice) session.
>
> In you example below, given that you have only allocated two /30s out of the
> /18 .... the BCP would be to advertise only the /18. Nothing more specific
> than the /18. So you would have (assuming the /18 is 202.9.0/18):
>
> router bgp 1076
> no auto-summary
> no synchronization
> neighbor a.b.c.d remote-as x
> neighbor a.b.c.d prefix-list out-filter out
> network 202.9.0.0 mask 255.255.192.0
> !
> ip route 202.9.0.0 255.255.192.0 Null 0 250
> !
> ip prefix-list out-filter permit 202.9.0.0/18
> ip prefix-list out-filter deny 0.0.0.0/0 le 32
> !
>
> There are three major techniques for advertising you aggregate to your
> upstream. (see the first BGP session in the BGP Workshop materials). We
> recommend this one in the workshop. We've found - through experience - to be
> the easiest for young ISPs to implement.
>
> On the NAT question, is the public addresses inside the /18 allocation? If
> not, the easiest thing to do is to to renumber the public NAT address pool
> to the /18 block.
>
> Now for the interesting recommendation. If you check out IP Unnumbered and
> still decided to use the /30 technique, we recommend that these /30s NOT go
> into your IGP. The would be advertised and generated into your iBGP. Why?
> Consider these routes as "external" to your network. "External" routes are
> the job of the EGP (BGP in this case). By keeping these external routes out
> of the IGP, you help keep the IGP lean - increasing the convergence time
> (recovery speed) of you network.
>
> This may not seem like a big deal when you have two /30 links. But, it is a
> big deal when you have 10,000 /30 links in your IGP.
>
> Now some would say that you can use the synergistic relationship of your
> routing protocol, addressing plan, and network plan to insure that you do
> IGP summarization at the area border router. This is the goal in an ideal
> network. It is what we teach. But .... I have yet to see any network that
> keep the discipline to insure summarization would happen. Scaling, growth,
> and customer pressures eventually forces the wholes to be punched into the
> summarizations - allow /30s all over the place.
>
> This is the key reason we recommend IP Unnumbered. With IP Unnumbered, you
> can have 10,000 lease line customer - with no IGP entries on the circuits
> between you and your customer.
>
> Check out the workshop materials. We have this covered in the materials.
>
> Barry
> -----Original Message-----
> From: Vinod Anthony Joseph Cherunni [mailto:vac@antarix.net]
> Sent: Friday, February 02, 2001 11:13 PM
> To: cisco-nsp@puck.nether.net
> Subject: [nsp] BGP Advertisements
>
>
>
> Dear All,
>
> Once again some queries in my mind. Out of a /18 address block that has
> been allocated to me, which I am further subnetting to achieve multiple /30
> prefixes to allocate addresses for all my links. The following queries arise
> in my mind.
>
> (a) How would I announce those /30 prefixes to an upstream provider. I
> mean that If I am using the following /24 block "202.9.4.0/24" to break it
> into multiple /30 prefixes which would effectively give me 64 of such
> prefixes, & assuming only two /30 prefixes are put into use.. This means
> that only two /30 prefixes will be in my IGP routing table. Now how will I
> aggregate these multiple /30 prefixes into a single probably /24 block &
> announce it
>
> If I have currently only allocated 202.9.4.4/30 & 202.9.4.8/30 for two
> links & the remaining /30 prefixes are unused. Can I summarize them as
> follows in BGP
>
> router bgp 1076
> no auto-summary
> no synchronization
> neighbor a.b.c.d remote-as x
> aggregate-address 202.9.4.0 255.255.255.0 summary-only (Is this okay or
> else will I have to list the two /30's using "network" statements. Feel it
> won't scale since the number will grow large.)
>
> (b) Also I am starting off with using private addresses at small portions
> of my internal network due to some reasons, & use NAT for translating an
> internal private IP Prefix to a valid IP /24 prefix. How could I announce it
> to an external peer. Because I would'nt have any entry in the internal
> routing table for the NAT public prefix.
>
> (c) Lastly is it advicable to announce the entire /18 allocated to me
> using an ip route to null for the entire /18 even though its not being fully
> utilized, if I would need to do that.
>
>
> Kindly enlighten me.
>
> With warm regards,
>
> Vinod.
>
>
> ------=_NextPart_000_0240_01C08DB9.DB90CCE0
> Content-Type: text/html;
> charset="iso-8859-1"
> Content-Transfer-Encoding: quoted-printable
>
> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
> <HTML><HEAD>
> <META http-equiv=3DContent-Type content=3D"text/html; =
> charset=3Diso-8859-1">
> <META content=3D"MSHTML 5.50.4611.1300" name=3DGENERATOR></HEAD>
> <BODY>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>Hello=20
> Vinod,</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>Why=20
> are you using /30s that take up address space and increase the size of =
> your IGP?=20
> Use IP Unnumbered. IP Unnumbered is the BCP of running an Internet=20
> operations.</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>As to=20
> your question below, use the following as =
> references:</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>ISP=20
> Essentials Power Session</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2> <A=20
> href=3D"http://www.cisco.com/public/cons/isp/documents/IOSEssentials_Semi=
> nar.zip">http://www.cisco.com/public/cons/isp/documents/IOSEssentials_Sem=
> inar.zip</A></FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>BGP=20
> Routing Workshop</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2> <A=20
> href=3D"http://www.cisco.com/public/cons/workshops/bgp/">http://www.cisco=
> .com/public/cons/workshops/bgp/</A></FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>In the=20
> BGP Routing Workshop, look specifically for the BCP (Best Common =
> Practice)=20
> session. </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>In you=20
> example below, given that you have only allocated two /30s out of the =
> /18 ....=20
> the BCP would be to advertise only the /18. Nothing more specific than =
> the /18.=20
> So you would have (assuming the /18 is 202.9.0/18):</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial size=3D2>router =
> bgp 1076=20
> <BR>no auto-summary <BR>no synchronization <BR>neighbor a.b.c.d =
> remote-as x=20
> </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><SPAN lang=3DEN-GB=20
> style=3D"FONT-SIZE: 88%; COLOR: #006c88; FONT-FAMILY: 'Courier New'; =
> mso-color-index: 4"><FONT=20
> face=3DArial color=3D#000000 size=3D2>neighbor a.b.c.d prefix-list =
> out-filter out=20
> </FONT></SPAN>
> <DIV style=3D"mso-line-spacing: '100 50 0'; mso-margin-left-alt: =
> 191"><SPAN=20
> style=3D"DISPLAY: none; mso-special-format: lastCR"></SPAN></DIV><FONT =
> face=3DArial=20
> size=3D2>network 202.9.0.0 mask 255.255.192.0</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial=20
> size=3D2>!</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial size=3D2>ip =
> route 202.9.0.0=20
> 255.255.192.0 Null 0 250</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial=20
> size=3D2>!</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001></SPAN><SPAN =
> class=3D975343415-03022001><FONT=20
> face=3D"Courier New"><SPAN lang=3DEN-GB=20
> style=3D"FONT-SIZE: 88%; COLOR: #006c88; FONT-FAMILY: 'Courier New'; =
> mso-color-index: 4"><FONT=20
> face=3DArial color=3D#000000 size=3D2>ip prefix-list out-filter permit =
> 202.9.0.0/18=20
> </FONT></SPAN></DIV>
> <DIV>
> <DIV class=3DO style=3D"tab-interval: .9322in" v:shape=3D"_x0000_s3074">
> <DIV style=3D"mso-line-spacing: '95 50 0'; mso-margin-left-alt: =
> 191"><SPAN=20
> lang=3DEN-GB=20
> style=3D"FONT-SIZE: 88%; COLOR: #006c88; FONT-FAMILY: 'Courier New'; =
> mso-color-index: 4"><FONT=20
> face=3DArial color=3D#000000 size=3D2>ip prefix-list out-filter deny =
> 0.0.0.0/0 le 32=20
> </FONT></SPAN></DIV>
> <DIV style=3D"mso-line-spacing: '95 50 0'; mso-margin-left-alt: =
> 191"><SPAN=20
> lang=3DEN-GB=20
> style=3D"FONT-SIZE: 88%; COLOR: #006c88; FONT-FAMILY: 'Courier New'; =
> mso-color-index: 4"><SPAN=20
> class=3D975343415-03022001><FONT face=3DArial color=3D#000000=20
> size=3D2>!</FONT></SPAN></SPAN></DIV>
> <DIV style=3D"mso-line-spacing: '100 50 0'; mso-margin-left-alt: =
> 191"><FONT=20
> face=3DArial color=3D#0000ff size=3D2></FONT></FONT></SPAN><SPAN=20
> class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff=20
> size=3D2></FONT></SPAN> </DIV></DIV></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>There=20
> are three major techniques for advertising you aggregate to your =
> upstream. (see=20
> the first BGP session in the BGP Workshop materials). We recommend this =
> one in=20
> the workshop. We've found - through experience - to be the easiest for =
> young=20
> ISPs to implement. </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>On the=20
> NAT question, is the public addresses inside the /18 allocation? If not, =
> the=20
> easiest thing to do is to to renumber the public NAT address pool to the =
> /18=20
> block. </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>Now=20
> for the interesting recommendation. If you check out IP Unnumbered and =
> still=20
> decided to use the /30 technique, we recommend that these /30s NOT go =
> into your=20
> IGP. The would be advertised and generated into your iBGP. Why? Consider =
> these=20
> routes as "external" to your network. "External" routes are the job of =
> the EGP=20
> (BGP in this case). By keeping these external routes out of the IGP, you =
> help=20
> keep the IGP lean - increasing the convergence time (recovery speed) of =
> you=20
> network.</FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>This=20
> may not seem like a big deal when you have two /30 links. But, it is a =
> big deal=20
> when you have 10,000 /30 links in your IGP. </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>Now=20
> some would say that you can use the synergistic relationship of your =
> routing=20
> protocol, addressing plan, and network plan to insure that you do IGP=20
> summarization at the area border router. This is the goal in an ideal =
> network.=20
> It is what we teach. But .... I have yet to see any network that keep =
> the=20
> discipline to insure summarization would happen. Scaling, growth, and=20
> customer pressures eventually forces the wholes to be punched into =
> the=20
> summarizations - allow /30s all over the place. </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>This=20
> is the key reason we recommend IP Unnumbered. With IP Unnumbered, you =
> can have=20
> 10,000 lease line customer - with no IGP entries on the circuits between =
> you and=20
> your customer. </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
> size=3D2>Check=20
> out the workshop materials. We have this covered in the materials.=20
> </FONT></SPAN></DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2></FONT></SPAN> </DIV>
> <DIV><SPAN class=3D975343415-03022001><FONT face=3DArial color=3D#0000ff =
>
> size=3D2>Barry</FONT> </SPAN></DIV>
> <BLOCKQUOTE=20
> style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px =
> solid">
> <DIV class=3DOutlookMessageHeader dir=3Dltr align=3Dleft><FONT =
> face=3DTahoma=20
> size=3D2>-----Original Message-----<BR><B>From:</B> Vinod Anthony =
> Joseph=20
> Cherunni [mailto:vac@antarix.net]<BR><B>Sent:</B> Friday, February 02, =
> 2001=20
> 11:13 PM<BR><B>To:</B> cisco-nsp@puck.nether.net<BR><B>Subject:</B> =
> [nsp] BGP=20
> Advertisements<BR><BR></FONT></DIV><BR><FONT face=3D"Courier New" =
> size=3D2>Dear=20
> All,</FONT> <BR><BR><FONT face=3D"Courier New" size=3D2>Once again =
> some queries in=20
> my mind. Out of a /18 address block that has been allocated to me, =
> which I am=20
> further subnetting to achieve multiple /30 prefixes to allocate=20
> addresses for all my links. The following queries arise in my =
> mind.</FONT>=20
> <BR><BR><FONT face=3D"Courier New" size=3D2>(a) How would I announce =
> those /30=20
> prefixes to an upstream provider. I mean that If I am using the =
> following /24=20
> block "202.9.4.0/24" to break it into multiple /30 prefixes which =
> would=20
> effectively give me 64 of such prefixes, & assuming only two /30 =
> prefixes=20
> are put into use.. This means that only two /30 prefixes will be in my =
> IGP=20
> routing table. Now how will I aggregate these multiple /30 prefixes =
> into a=20
> single probably /24 block & announce it</FONT> <BR><BR><FONT=20
> face=3D"Courier New" size=3D2>If I have currently only allocated =
> 202.9.4.4/30=20
> & 202.9.4.8/30 for two links & the remaining /30 prefixes are =
> unused.=20
> Can I summarize them as follows in BGP</FONT> <BR><BR><FONT =
> face=3D"Courier New"=20
> size=3D2>router bgp 1076</FONT> <BR><FONT face=3D"Courier New" =
> size=3D2>no=20
> auto-summary</FONT> <BR><FONT face=3D"Courier New" size=3D2>no=20
> synchronization</FONT> <BR><FONT face=3D"Courier New" =
> size=3D2>neighbor a.b.c.d=20
> remote-as x</FONT> <BR><FONT face=3D"Courier New" =
> size=3D2>aggregate-address=20
> 202.9.4.0 255.255.255.0 summary-only <B>(Is this okay or else will I =
> have to=20
> list the two /30's using "network" statements. Feel it won't scale =
> since the=20
> number will grow large.)</B></FONT> <BR><BR><FONT face=3D"Courier New" =
>
> size=3D2>(b) Also I am starting off with using private addresses at =
> small=20
> portions of my internal network due to some reasons, & use NAT for =
>
> translating an internal private IP Prefix to a valid IP /24 prefix. =
> How could=20
> I announce it to an external peer. Because I would'nt have any entry =
> in the=20
> internal routing table for the NAT public prefix.</FONT> <BR><BR><FONT =
>
> face=3D"Courier New" size=3D2>(c) Lastly is it advicable to announce =
> the entire=20
> /18 allocated to me using an ip route to null for the entire /18 even =
> though=20
> its not being fully utilized, if I would need to do that.</FONT>=20
> <BR><BR><BR><FONT face=3D"Courier New" size=3D2>Kindly enlighten =
> me.</FONT>=20
> <BR><BR><FONT face=3D"Courier New" size=3D2>With warm regards,</FONT>=20
> <BR><BR><FONT face=3D"Courier New" size=3D2>Vinod.</FONT>=20
> <BR></BLOCKQUOTE></BODY></HTML>
>
> ------=_NextPart_000_0240_01C08DB9.DB90CCE0--
>
>
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:27 EDT