From: Howard C. Berkowitz (hcb@xxxxxxxxxxxx)
Date: Mon Mar 11 2002 - 16:45:14 GMT-3
At 1:54 PM -0500 3/11/02, Mannan Venkatesan wrote:
>Ok, I have a question here. You said "redistribute bar information, with
>filters y and foo metric x, into foo". 'Distribute-list y in' command only
>control what is going to go to your local router's routing table.
Actually, it doesn't even do that. It filters what goes into the
specific routing process' tables. The output of that routing table
with other sources of routing information for installation in the
main RIB.
>It doesn't
>filter what is going to go other routers.
>
>router eig 1
>red osp 1 def x
>distribute-list 1 in
>
>This will filter routes getting into local router's routing table based on
>acl 1. But it will not filter what is being sent to other eig neighbors
>So, is "distribute-list in" import???
Yes, with respect to the local router
>
>And again, distribute-list 1 out osp 1 will control the routes being
>imported from ospf to eigrp. So, is distribute-list out "import" here?
>Confused,enough???
It's export with respect to ospf, but import with respect to eigrp.
The redistribute command just doesn't have the fine granularity to
make it unambiguous.
Here's some material from the draft of my upcoming Wiley book,
_Building Service Provider Networks_ (sorry, it's much more readable
with formatting)
Policy Notation with RPSL
-------------------------
RPSL is the only standards-based routing policy notation. Tools have
been written to generate specific router configuration statements
from it.
This discussion of notation is not intended as a complete tutorial on
the languages involved. Rather, it is intended to give a sense of
their capabilities.
Information flow in RPSL is defined with respect to peering
specifications. Most often, peering specifications are of the
granularity of AS to AS. They can, however, be refined to
information flow at specific router interfaces, or broadened to
define policy to multiple AS. The most general form of the peering
specification allows the possibility of exchanging information
between routing protocols, although BGP is the default.
The full power of import and export expressions involves the
capability of interacting among different routing protocols, not just
BGP.
Table 1: Import Peering Expression (from the RPSL specification)
import: [protocol <protocol-1>] [into <protocol-2>]
from <peering-1>
AS-SETs are not the only kind of set you can define, and you can use
recursion for each type.
Route-sets include multiple prefixes:
A fairly complex example is the peering-set:
peering-set: prng-bar
peering: AS1 at 9.9.9.1
peering-set: prng-foo
peering: prng-bar
peering: AS2 at 9.9.9.1
aut-num: AS1
import: from prng-foo accept { 128.9.0.0/16 }
--------
Contrast Cisco, RPSL, and Juniper:
--------
JunOS has a specific policy construct that differs from RPSL, but has
some of the same structured characteristics. Its syntax is
consistent with the general JunOS style, which draws from FreeBSD
UNIX configuration language.
There are two primary ways to use policy with JunOS. Our principal
focus here is on BGP acceptance and advertising policies. JunOS
policy expressions, however, also can be used to control the
exporting of routes out of the main RIB, into, for example, OSPF and
ISIS.
You write policies per routing protocol, using the policy-option
construct. Most of the detailed policy matching and action
conditions are in the policy-statement policy-name inside the
policy-option structure, but are preceded by information about
as-path, community, and damping.
policy-options {
as-path name regular-expression;
community name members [community-ids];
damping name {
half-life minutes;
max-suppress minutes;
reuse number;
suppress number;
}
policy-statement policy-name {
term term-name {
from {
match-conditions;
route-filter destination-prefix match-type <actions>;
prefix-list name;
}
to {
match-conditions;
}
then actions;
}
}
prefix-list name {
ip-addresses;
}
For individual policy expressions, you can combine unitary and set AS
information with the Boolean operators AND, OR, and EXCEPT.
The EXCEPT operator
EXCEPT is the operator for set subtraction, and is equivalent to AND
NOT. ((AS1 OR AS2) EXCEPT AS2), for example, equals AS1.
>
>Mannan
>
>
>----- Original Message -----
>From: "Howard C. Berkowitz" <hcb@gettcomm.com>
>To: <ccielab@groupstudy.com>
>Sent: Monday, March 11, 2002 11:27 AM
>Subject: Re: distribute-list
>
>
>> A general comment here that might help in understanding.
>>
>> "Redistribution" is a Cisco term that is rather awkward, but has been
>> adopted by the industry. There are less ambiguous terms I'll mention
>> in a minute.
>>
>> But I like to explain what "redistribute" means by expanding the grammar:
>>
>> router foo
>> redistribute bar default-metric x
>> distribute-list y in
>>
>> means
>>
>> redistribute bar information, with filters y and foo metric x, into
>foo.
>>
>> The more general terms are import and export. Redistribution is
>importing:
>>
>> import bar into foo [optional filters and actions]
>>
>> Export is like a distribute-list out.
>>
>>
>>
>> At 7:09 AM -0800 3/11/02, Bhisham Bajaj wrote:
>> >mannan
>> >
>> >thank u
>> >
>> >i got the point and by now know how wrong i was in
>> >understanding redistribution
>> >
>> >thank u
>> >Reg
>> >bajaj
>> >
>> >--- Mannan Venkatesan <mv70@lucent.com> wrote:
>> >> Bajaj,
>> >> Yigit is correct. "out" option works differently
>> >> when you use it with a RP.
>> >> If you use it with interface, it will filter the
>> >> routes sending out of that
>> >> interface.
>> >>
>> >> It you use it with RP, it will filter the routes
>> >> from the RP being
>> >> redistributed.
>> >>
>> >> HTHs,
>> >> Mannan
>> >>
>> >>
>> >> ----- Original Message -----
>> >> From: "A Yigit Zorlu" <alec_cisco@yahoo.com>
>> >> To: "'Bhisham Bajaj'" <bhishambajaj@yahoo.com>;
>> >> "'Mannan Venkatesan'"
>> >> <mv_lab@hotmail.com>; "'lab'"
>> >> <ccielab@groupstudy.com>
>> >> Sent: Monday, March 11, 2002 1:48 AM
>> >> Subject: RE: distribute-list
>> >>
>> >>
>> >> > Hi,
>> >> >
>> >> > If you would using distribute-list 1 out serial 0
>> >> you were correct. But in
>> >> > this case it filters routes coming out of EIGRP
>> >> into OSPF. Same for
>> >> > connected. Same for IPX as well
>> >> >
>> >> > ipx nlsp
>> >> > redistribute eigrp 1
>> >> > distribute-list 7 out eigrp 1
>> >> > from EIGRP into NLSP.
>> >> >
>> >> > Thanks,
>> >> >
> > >> > Yigit
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