From: Jerry (phase90@comcast.net)
Date: Tue Feb 25 2003 - 21:28:57 GMT-3
To me RIP is an ip routing protocol which functions by sending and receiving
UDP / ip datagrams.
Jerry
----- Original Message -----
From: Howard C. Berkowitz <hcb@gettcomm.com>
To: <ccielab@groupstudy.com>
Sent: Tuesday, February 25, 2003 3:50 PM
Subject: RE: split-horizon & BGP
> At 1:52 PM -0500 2/25/03, OhioHondo wrote:
> >Peter
> >
> >For troubleshooting purposes I find it handy to have an idea of where in
the
> >ISO stack a problem might exist. In this e-mail string someone suggested
RIP
> >runs over UDP. I don't believe that to be true
>
> AFAIK, I may have been the only person to say that. Why do you think
> it's untrue?
>
> UDP Port 520. See the RFC. Do I need to get a note from Charley
> Hedrick or Gary Malkin?
>
>
>
> "RIP is a UDP-based protocol. Each host that uses RIP has a routing
> process that sends and receives datagrams on UDP port number 520.
> All communications directed at another host's RIP processor are sent
> to port 520. All routing update messages are sent from port 520.
> Unsolicited routing update messages have both the source and
> destination port equal to 520. Those sent in response to a request
> are sent to the port from which the request came. Specific queries
> and debugging requests may be sent from ports other than 520, but
> they are directed to port 520 on the target machine."
>
>
> >and if it is not true then
> >this can be mis-leading to someone that is trying to understand the
> >technology. As far as passing the test, it may not be necessary to
> >absolutely know how something works.
>
> What do you mean "how something works?" If you mean what protocols
> run over what, you'd better know that unless you want weird and
> wonderful results from access lists.
>
> But trying to coerce a concept NOT developed with OSI in mind into
> the OSI reference model has nothing to do either with why something
> is designed (theory) or how it works (principles).
>
> >
> >I send my perceptions out to this forum to be corrected if I am wrong.
That
> >helps me learn. If I am right then I am helping someone else in their
> >pursuit to understand the technology -- for the test and for practical
use.
> >;)
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> >Peter van Oene
> >Sent: Tuesday, February 25, 2003 11:31 AM
> >To: ccielab@groupstudy.com
> >Subject: RE: split-horizon & BGP
> >
> >
> >At 09:59 AM 2/25/2003 -0500, OhioHondo wrote:
> >>Howard
> >>
> >>I disagree with your "BGP is not an application" statement. The fact
that
> >it
> >>uses TCP means it uses Layer 4. The fact that it uses TCP ports means
that
> >>it uses Layer 5 and it creates TCP sessions (Layer 6) with a
communicating
> >>partner.
> >
> >These discussions about which OSI layer an IP protocol fits into are
really
> >quite fruitless. Conformance with OSI terminology was not a design goal
> >for BGP as far as I know.
> >
> >
> >>It is an entity communicating over a session and through the network. If
> >>that's not a definition of a Layer 7 (application) entity I don't know
what
> >>is ;)
> >>
> >>
> >>-----Original Message-----
> >>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> >>Howard C. Berkowitz
> >>Sent: Monday, February 24, 2003 9:54 PM
> >>To: ccielab@groupstudy.com
> >>Subject: RE: split-horizon & BGP
> >>
> >>
> >>At 5:20 PM -0500 2/24/03, Jerry Haverkos wrote:
> >> >Howard
> >> >
> >> >I do not believe that the is a command to turn split-horizon on or
off
> >> >available for BGP, especially not one that works at layer 3.
> >>
> >>First, let me be clear about some terminology and OSI references,
> >>which you may know.
> >>
> >>BGP is not an application. It is a connection-oriented network layer
> >>control program. That it happens to use reliable layer 4 transport
> >>is irrelevant to its payload function, which is totally network layer
> >>oriented. Connection-oriented routing protocol, connection-oriented
> >>transport mechanism.
> >>
> >>Split horizon is not a general problem of DV protocols, but of
> >>connectionless transports for the routing information. Split horizon
> >>also applies to routes, not link state information.
> >>
> >>It can be perfectly normal behavior to receive a self-originated LSA
> >>or LSP at a LS interface. Split horizon isn't needed because there
> >>are tiebreakers such as age.
> >>
> >>RIP and IGRP are multicast/broadcast and can cause loops if split
> >>horizon is not enforced. Since EIGRP first forms neighbor
> > >relationships and uses reliable transport, the split horizon issue is
> >>not nearly as significant. In any case, EIGRP has superior loop
> >>prevention mechanisms.
> >>
> >>Think of what the AS_PATH would look like if BGP returned an update
> >>to the AS from which it received it. There would be a loop in it,
> >>and it would be discarded. It definitely would be discarded at the
> >>receiver, and it's an implementer choice to check for loops before
> >>sending.
> >>
> >>
> >> >My point is
> >> >that BGP does not run at the layer 2 or layer 3 or even layer 4 part
of
> >the
> >> >stack.
> >>
> >>BGP _payloads_ do run in the management plane at layer 3, as do all
> >>other routing protocols. RIP, for example, runs over UDP, but again
> >>contains only layer 3 management information.
> >>
> >> >It is an application that exchanges data via an established BGP TCP
> >> >session. It is an application to application (BGP peer to peer)
decision
> >>not
> >> >to send routes back to a peer that it received the routes from.)
> >> >
> >> >I do not believe that it has anything to do with the traditional idea
> >that
> >> >split horizon does not allow updates, received over an interface, to
be
> >>sent
> >> >back over that interface. ;)
> >> >
> >> >-----Original Message-----
> >> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf
Of
> >> >Howard C. Berkowitz
> >> >Sent: Monday, February 24, 2003 3:13 PM
> >> >To: ccielab@groupstudy.com
> >> >Subject: RE: split-horizon & BGP
> >> >
> >> >
> >> >At 12:30 PM -0500 2/24/03, OhioHondo wrote:
> >> >>Since BGP runs as a higher layer protocol (on top of TCP) split
horizon
> >> >does
> >> >>not apply.
> >> >
> >> >Why do you think TCP would make a difference in loop detection?
> >> >
> >> >BGP is not strictly a DV protocol. Its primary loop detection method
> >> >is examining incoming AS paths (i.e., path vectors) and rejecting
> >> >those that contain the local AS number.
> >> >
> >> >There are additional methods, for iBGP using confederations and RR's,
> >> >to reduce/eliminate transient internal loops/oscillation, but these
> >> >are probably outside the CCIE scope.
> >> >
> >> >It isn't completely clean, as BGP/PV is provably loop-free only when
> >> >additional policies are NOT used.
> >> >
> >> >>
> >> >>-----Original Message-----
> >> >>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf
Of
> >> >>Pedro Eira
> >> >>Sent: Monday, February 24, 2003 10:36 AM
> >> >>To: ccielab@groupstudy.com
> >> >>Subject: split-horizon & BGP
> >> >>
> >> >>
> >> >>Hello, Would split-horizon have any effect on BGP?Should I follow
the
> >> >>same rules for BGP as I do for other DV routing protocols when
> >> >>split-horizon is involved?
This archive was generated by hypermail 2.1.4 : Sat Mar 01 2003 - 11:06:35 GMT-3