Subject: Re: BGP4 questions
From: John Krawczyk <[email-masked]>
To: [email-masked]
Date: Fri, 26 Jul 96 09:21:05 EDT

On Thu, 25 July, Cristina Radulescu-Banu ([email-masked]) wrote:

   	Hi. I have 2 questions:
   
   	1. What does this means:
   
   	A BGP speaker needs to be able to support disabling
   advertisement of external border routers. (RFC 1771, page 22)

   	2. Did someone actually implement this?

Cristina,

I had to look at the spec to put this into context.  This is in the
section talking about the NEXT_HOP path attribute, and concerns what is
sometimes referred to as "third party" advertisement.  That is, if
routers A, B, and C are all on the same multi-access network, A can
advertise B's NLRI to C using "B" as the NEXT_HOP, so as to avoid
sending packets out onto the same subnet twice (C->B instead of
C->A->B).  This is the default behavior in our implementation.

I can think of two interpretations for "disabling" this:

1) Have A use its own address as NEXT_HOP.  This would be necessary over
an NBMA network where there is no direct connectivity between B and C.
I can't think of any other good reason for doing it (that doesn't mean
that there aren't other good reasons... :).

2) Prevent A from advertising B's routes to C.  You might want to do
this to save memory, but you are also sacrificing a backup mechanism for
forwarding from C to B.

You can do all of this in our implementation through BGP policies.  It's
not as easy as just turning a knob to say "don't do that".

-jj
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Date: Thu, 25 Jul 1996 14:55:30 -0400
From: Cristina Radulescu-Banu <[email-masked]>
To: [email-masked]
Subject: BGP4 questions
Sender: [email-masked]
Reply-To: [email-masked]

	Hi. I have 2 questions:

	1. What does this means:

	A BGP speaker needs to be able to support disabling
advertisement of external border routers. (RFC 1771, page 22)

	2. Did someone actually implement this?

	Thanks,

					Cristina

-- 

...............................................................................
Cristina Radulescu-Banu : Midnight Networks 200 Fifth Avenue Waltham MA 02154
[email-masked]  : Vox 617/890-1001 Fax 0028 The Best in Network Software
	
	 There wouldn't be wolves if there wouldn't be sheep.

			  - Romanian proverb

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To: [email-masked]
Cc: [email-masked]
Subject: Re: Where to find BGP 
Date: Tue, 09 Jul 1996 18:04:29 -0400
From: Curtis Villamizar <[email-masked]>
Sender: [email-masked]
Reply-To: [email-masked]

In message <[email-masked]>, rewind@
phish.nether.net writes:
>     Pardon me if this is a little trivial or whatnot but I have tried to
> work with teh Border Gateway Protocol and have found few places that use
> BGP.  If someone could email me where I might be able to actually talk to
> a BGP speaker, I would be obliged.  Again, sorry for any unnecessary
> traffic.

Try your internet service provider.  Looks to me like Michnet who in
turn talks to MCI using BGP who talks to us via BGP.

traceroute -q 2 phish.nether.net
traceroute to phish.nether.net (198.108.59.2), 30 hops max, 40 byte packets
 1  e0.enss470.t3.ans.net (204.148.1.30)  1.788 ms  2.159 ms
 2  s1-0.cnss52.Hartford.t3.ans.net (192.103.65.9)  27.257 ms  27.475 ms
 3  mf0.cnss48.Hartford.as690.ans.net (140.222.48.222)  27.123 ms  26.722 ms
 4  ft1.cnss43.Cleveland.as690.ans.net (140.222.43.3)  43.535 ms  41.491 ms
 5  border3-fddi1-0.NorthRoyalton.mci.net (206.157.77.9)  43.671 ms  44.19 ms
 6  core1-fddi-0.NorthRoyalton.mci.net (204.70.98.17)  43.434 ms  42.906 ms
 7  core-hssi-2.Chicago.mci.net (204.70.1.93)  51.701 ms  50.577 ms
 8  border1-fddi-0.Chicago.mci.net (204.70.2.82)  50.459 ms  51.538 ms
 9  merit-michnet-ds3.Chicago.mci.net (204.70.24.6)  55.384 ms  56.059 ms
10  fdd0.michnet1.mich.net (192.203.195.4)  55.394 ms  55.352 ms
11  eth1.iti.mich.net (198.108.90.78)  55.823 ms  58.971 ms
12  free-lan.cic.net (192.131.22.30)  57.969 ms  58.274 ms
13  phish.nether.net (198.108.59.2)  59.977 ms  58.384 ms

show ip bgp_routes 198.108.59.2
Network/Mask       Peer Rem Addr   NextHop Address Org Loc Pref   B/U Sl
------------------ --------------- --------------- --- ---------- --- --
198.108.0.0/14     140.223.40.62   206.157.77.9    IGP        102 B/U  6
        As Path: <3561 237>

AS3561 is MCI.  AS237 is Michnet.

Curtis
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Date: Tue, 9 Jul 1996 14:22:17 -0400 (EDT)
From: <[email-masked]>
To: [email-masked]
Subject: Where to find BGP
Sender: [email-masked]
Reply-To: [email-masked]

    Pardon me if this is a little trivial or whatnot but I have tried to
work with teh Border Gateway Protocol and have found few places that use
BGP.  If someone could email me where I might be able to actually talk to
a BGP speaker, I would be obliged.  Again, sorry for any unnecessary
traffic.

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From: [email-masked]
Date: 03 Jul 96 23:44:21 EDT
To: BGP Working Group <[email-masked]>, John Moy          <[email-masked]>, OSPF Working Group <[email-masked]>
Subject: Addr: Re: Addr: An Additional Looping Problem
Comments: Resending note of Tue, 2 Jul 1996 16:01:17 -0400 from [email-masked] (John Moy) <SMTP2 AT IINUS1>
Sender: [email-masked]
Reply-To: [email-masked]

*** Resending note of 07/02/96 16:02
>Date: Tue, 2 Jul 1996 16:01:17 -0400
>From: [email-masked] (John Moy)
>Subject: Re: Addr: An Additional Looping Problem

>Richard-

>I think that you are taking the BGP specification too literally. When
>using "IGP distance is used as tie-breaker", you take the border
>router which is closer according to the IGP. In OSPF, intra-area
>routes are always "closer" than inter-area routes. So there is no problem.

>John

John,

(I've added the bgp list to the conversation).

I think that I agree that BGP must use the IGP rules for determining
closest nexthop, not just compare IGP metrics; otherwise, one may get
routing loops. For OSPF this means (during the BGP "IGP distance
tie breaker") an intra-area route to one BGP nexthop is "closer" than
an inter-area route to another BGP nexthop, which is "closer" than
an ASE route to a third BGP nexthop, etc., in spite of relative OSPF
costs. I guess similar reasoning would apply for BGP/ISIS.

I'll note that I am not the only one to read this part of the spec "too
literally". Ciscos (at least release 10.3.x) will prefer (by tie-breaker)
a BGP nexthop with an OSPF ASE type 2 route to a BGP nexthop with an OSPF
intra-area route, if the ASE external cost is low enough. Gated
(which doesn't use OSPF ASEs to resolve nexthops, yet) will prefer
a BGP nexthop with an inter-area route to a BGP nexthop with an
intra-area route, if the inter-area route metric is low enough.

-- Richard Woundy, [email-masked]

P.S. For BGP mailing list readers, the route loop can occur when
  the same destination prefix is announced to two routers in
  the same OSPF AS (but within different areas), given certain link
  configurations and metrics.

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From: Masataka Ohta <[email-masked]>
Subject: Re: shortcut routing
To: [email-masked] (Andrew G. Malis)
Date: Wed, 3 Jul 96 11:54:11 JST
Cc: [email-masked], [email-masked], [email-masked], [email-masked], [email-masked], [email-masked]
Sender: [email-masked]
Reply-To: [email-masked]

> > and fatal bug that they have discovered? Any comments are welcome.
> 
> Not "fatal", really

Sure. It's mostly fatal. Moreover, it is not a bug. So, bug fixing
is impossible. See draft-ohta*mcast* for details.

NHRP can still survive in unicast X.25 environment.

						Masataka Ohta
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Date: Tue, 02 Jul 1996 18:26:32 -0500
To: [email-masked]
From: Bob Everson <[email-masked]>
Subject: Re: shortcut routing
Cc: [email-masked], [email-masked], [email-masked], [email-masked]
Sender: [email-masked]
Reply-To: [email-masked]

At 11:15 AM 7/2/96 +0200, Sarunas Koncius wrote:
>Hello,
>
>Does anybody remember something what was happening few years ago
>about shortcut routing,
 
Sounds like NHRP.

Try  ftp://ftp.nexen.com/pub/ion/draft-ietf-rolc-nhrp-08.txt

>some IETF working group on that (which seems

Was ROLC, now ROLC and IP-ATM are combined into ION.

>not to exist now) and fatal bug what they have discovered? Any
>comments are welcome.
>
>Sarunas Koncius
>

Bob 

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To: [email-masked]
Cc: [email-masked], [email-masked], [email-masked], [email-masked], [email-masked]
Subject: Re: shortcut routing 
Date: Tue, 02 Jul 1996 16:46:34 -0400
From: "Andrew G. Malis" <[email-masked]>
Sender: [email-masked]
Reply-To: [email-masked]

Sarunas,

> Does anybody remember something what was happening few years ago
> about shortcut routing

NHRP (NBMA Next Hop Resolution Protocol), see
draft-ietf-rolc-nhrp-08.txt.

> some IETF working group on that (which seems not to exist now)

Was rolc (Routing Over Large CLouds), now ion (Internetworking Over
NBMA); see
http://www.ietf.cnri.reston.va.us/html.charters/ion-charter.html and
ftp://ftp.nexen.com/pub/ion/.

> and fatal bug that they have discovered? Any comments are welcome.

Not "fatal", really - see draft-ietf-rolc-r2r-nhrp-01.txt for further
discussion.  To quote it, "[NHRP] constrains the ability of
determining the egress router to the destinations that are directly
connected to the egress router."  Otherwise, a stable routing loop
could form.  The draft "describes extensions to the NHRP that allow a
station to acquire and maintain the information about the egress
router without constraining the destination(s) to be directly
connected to the egress router."

I hope this helps!

Cheers,
Andy
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Comments: Authenticated sender is <[email-masked]>
From: "Sarunas Koncius" <[email-masked]>
Organization: ALNA Kaunas
To: [email-masked], [email-masked], [email-masked], [email-masked]
Date: Tue, 2 Jul 1996 11:15:26 +0200
Subject: shortcut routing
Priority: normal
Sender: [email-masked]
Reply-To: [email-masked]

Hello,

Does anybody remember something what was happening few years ago
about shortcut routing, some IETF working group on that (which seems
not to exist now) and fatal bug what they have discovered? Any
comments are welcome.

Sarunas Koncius
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