Subject: Several questions about the ERO

From: Gaitonde Anandprasanna <[email-masked]>
Date: Tue, 28 Nov 2000 03:00:42 +0530 (IST)

If u can remeber there was some discussion going on 
How to fill ERO object in case of RSVP-TE , but somehow i was unable to
ask my questions at that time.

I have the follwoing queries:

3 options had been considered:
1) Put the router ID of the routers. This does not work with routers
 having multiuple links and unnumbered interfaces.

First i would like to know how can we put the router ID in the ERO
subobject. If we see the format of the ERO subobject we can put IPV4
prefix, IPV6 prefix or AS Number inside that object .

so how can we put router id. Is it in IP address format???

2) Put in the egress interface of the routers on the path.
That is  remote IP addrress of each link .

But in case of unnumbered links how can we get the IP address of the
remote end.

PLease let me know this.  

And also i am confused as to how to do the following

Refer RSVP-TE draft Section 4.3.4.1 :

SElection of Next Hop:

5) Interior of the abstract nnode case:- Otherwise, the node slects the
next hop within the abstract node of the subobject ( which the node
belongs to) that is along the path to  the abstract node of the second
subobject ( which is the next abstract node). 

How can we do this ?? Please let me know. (Perhaps i am asking an
implentation question here...)

Thanx in advance

Pras

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From: David Charlap <[email-masked]>
Date: Mon, 27 Nov 2000 18:30:05 -0500

Gaitonde Anandprasanna wrote:
> How to fill ERO object in case of RSVP-TE , but somehow i was unable
> to ask my questions at that time.
> 

Most routers choose one of their interface IP addresses as a router ID. 
Even if some other address is manually configured, I think routing
protocols advertise these addresses.

With respect to multiple links and unnumbered interfaces, you can still
specify an ERO, but not with full precision.  You can still specify a
list of routers that the LSP must go through, although you won't be able
to specify specific links.  Since router IDs (as defined by OSPF and
ISIS) are 4-byte values just like IP addresses, the existing IPv4 prefix
subobject should work.

> But in case of unnumbered links how can we get the IP address of the

Via a local routing table.  If the required information doesn't exist
(meaning it wasn't learned via routing protocols and was not
configured), then there is no way to determine the next-hop interface
and a PathErr will be generated.

> 5) Interior of the abstract nnode case:- Otherwise, the node slects 
> the next hop within the abstract node of the subobject ( which the
> node belongs to) that is along the path to  the abstract node of the
> second subobject ( which is the next abstract node).
> 

If an ERO subobject doesn't uniquely specify a single next-hop (could be
a loose subobject, an AS number, a prefix shorter than /32, or other
reasons) then the switch must pick a next-hop using whatever means it
has.  I think most implementations will use the switch's local routing
table, possibly taking QoS requirements into account.

If the switch doesn't have a local routing table, then it will obviously
be unable to process a a subobject where the next-hop is ambiguous and
will generate a PathErr.

-- David