Re: [Isis-wg] CCAMP LC: draft-ietf-ccamp-isis-interas-te-extension-02.txt

[Mach Chen <[e-mail]>]

Hi Hannes,

Thanks for you questions!

Please see inline...

--------------------------------------------------
From: "Hannes Gredler" <[e-mail]>
Sent: Friday, July 18, 2008 9:06 PM
To: "Mach Chen" <[e-mail]>om>; "isis mailing list" <[e-mail]>
Cc: "David Ward" <[e-mail]>om>; "Adrian Farrel" <[e-mail]>uk>; 
"ALABS Brungard Deborah A" <[e-mail]>om>; "Ross Callon" 
<[e-mail]>et>; "Christian Hopps" <[e-mail]>rg>; 
<[e-mail]>
Subject: Re: [Isis-wg] CCAMP LC: 
draft-ietf-ccamp-isis-interas-te-extension-02.txt

> hi,
>
> i have a general question:
>
>  since IS-IS does not run on the border link between ASes, how
>  are the TE link attributes like (remote ASBR-ID, AS #, system-ID)
>  supplied ? -

The TE link attributes are supplied by manually configuration.

>
>  is this done by means of static configuration, i.e. prone
>  to misconfiguration and lack of diagnosing & tracking changes
>  in the neighboring AS ?

As stated in the document (Section 5), some of the TE link attributes( 
remote ASBR-ID, ASN) are obtained manually from a neighboring administration 
as part of commercial relationship, so the operators (both include 
neighboring and local administrations) have the responsibility to check the 
information carefully before it entered as configuration information at the 
ASBR responsible for adverting the inter-AS TE links.

And we are considering a Border Gateway Protocol (BGP) peering may exist 
between the two ASBRs and this could be used to detect inconsistencies in 
configuration( e.g. the AS #).

>
> and a specific question on the semantics of the System ID field:
>
>  why is this required at all ? - and what should be inserted if the
>  neighboring ASBR does not have a system-ID (e.g. it is running OSPF).

There is no any specific requirement for the System-ID in this document, the 
System ID is just one of the ISIS protocol fields. The operators could 
configure any unique value within their domain as the System-ID( e.g. Router 
ID ) based on their planning/deployment policy, even if the neighboring ASBR 
does not have a system-ID.

>
>  --
>
>  IMO the inter-AS reachability TLV should just announce an AS number
>  and the remote ASBR IDs as subTLV information.

No,
Just as the the Extended IS Reachability TLV(rfc 3784) defined for 
advertisement of intra-area TE links, the inter-AS reachability TLV defined 
in this document is used to advertise the TE link attributes of an inter-AS 
TE link, so just announce an AS number and the remote ASBR IDs is not 
enough, because an inter-AS link also has other TE link attributes as an 
intra-area TE link does, and such TE link attributes are needed when 
performing path computation.

>
> or am i missing something ?
>
> /hannes
>
> ---
>
> 3.1. Inter-AS Reachability TLV
>
>   The Inter-AS Reachability TLV has type 141 (which needs to be
>   confirmed by IANA see Section 6.1), it contains a data structure
>   consisting of:
>
>      7 octets of System ID and Pseudonode Number
>      3 octets of default metric
>      1 octet of control information, consisting of:
>         1 bit of flooding-scope information
>         1 bit of up/down information
>         6 bits reserved
>      1 octet of length of sub-TLVs
>      0-243 octets of sub-TLVs
>         where each sub-TLV consists of a sequence of:
>           1 octet of sub-type
>           1 octet of length of the value field of the sub-TLV
>           0-241 octets of value
>
>
> On Tue, Jul 15, 2008 at 11:43:44AM -0500, David Ward wrote:
> |    All -
> |
> |    The CCAMP WG would like any last call comments from the ISIS WG on:
> |
> | 
> [1]http://www.ietf.org/internet-drafts/draft-ietf-ccamp-isis-interas-te
> |    -extension-02.txt
> |    This last call will timeout July 30, 2008. Please cc this email with
> |    your comments.
> |    Thanks
> |    -DWard, CHopps
> |
> | References
> |
> |    1. 
> http://www.ietf.org/internet-drafts/draft-ietf-ccamp-isis-interas-te-extension-02.txt
>
> | _______________________________________________
> | Isis-wg mailing list
> | [e-mail]
> | https://www.ietf.org/mailman/listinfo/isis-wg
> 

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