Subject: [mpls] Egress Router?

From: priyanka gupta <[email-masked]>
Date: Sun, 9 Aug 2009 08:19:00 +0530 (IST)

Hi Vijaya,

Q : How can we find a router, if it is an Egress Router or not...?

As you have stated the RFC line "FEC refers to the  LSR itself" , It means the destination IP address of the session /LSP is the local IP address either interface or loopback address of the router, than the router is considered as the egress router for that session. 

Secondly, say already a LSP is established till Router-D and nexthop router is not running any signalling protocol(LDP/RSVP-TE), but the data packet is destined to the nexthop router to Router-D, then router-D will be considered as egress router for that FEC.

A router can be egree for a FEC and non-egress for other FEC.

Hope I had given answer to your query.

Regards,
Priyanka Gupta
Network Engineer

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Today's Topics:

  1. Egress Router? (Vijaya Ramaraju)

----------------------------------------------------------------------

Message: 1
Date: Thu, 06 Aug 2009 10:27:44 +0530
From: Vijaya Ramaraju <[email-masked]>
Subject: [mpls] Egress Router?
To: [email-masked]
Message-ID: <[email-masked]>
Content-Type: text/plain; charset="us-ascii"

Hi Team, 

This is Vijaya Rama Raju.

How can we find a router, if it is an Egress Router or not...?

1) I found in an RFC, if the FEC refers to the  LSR itself.. what does
this mean exactly?

2) The next hop router for the FEC is outside of the Label switching
Network... Means if the nexthop is not in the MPLS domain or if it
nexthop is in the peer list.
Correct me if I am wrong. 

------------------------------------------------------------------------------------------------------------------

And One more thing, In the attachment, if suppose there is a nexthop
after Egress router, which is not in MPLS domain, then the packet will
be forwarded using IP address. And the Label value 
which Egress router maps is either Explicit Null or Implicit Null. Now,
if the nexthop after the Egress is switched to MPLS domain, then
mappings between the nexthop and the egress will be, the nexthop will
send Explicit Null or Implicit Null to the egress router and the egress
router, will send it's label.

So, my doubt is, before the Nexthop switched to MPLS domain, the router
before Egress router receives a label either Explicit Null or Implicit
Null. But after the Nexthop switched to MPLS domain, the label mappings
between Egress and the router before it must be changed. 

Please help me in this regard...

Thanks and Regards

Vijaya Rama Raju Jampana 
Mobile: 9492755564 

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From: Vijaya Ramaraju <[email-masked]>
Date: Tue, 11 Aug 2009 17:16:55 +0530

Thanks for the information....Priyanka !!!

-----Original Message-----
From: priyanka gupta <[email-masked]>
To: [email-masked]
Subject: Re: Egress Router?
Date: Tue, 11 Aug 2009 16:35:12 +0530 (IST)
Mailer: YahooMailRC/1358.27 YahooMailWebService/0.7.289.15

Hi Vijay,
 
Your scenario answer is quite implememtataion dependent.
 
LDP when establish a LSP it gets the route from FIB or RIB(as per
implementation)
In your scenario,
CASE-1: LER2 is egress for say IP2 x.x.x.x address

RIB
Ip address            Nexthop           Interafce
xxxx                          IP router           say eth0 

LER2 has a knowledge that IP router is my next router with whom I dont
have LDP session.How it check and confirms is implementation
dependent.RFC doesnt take on this.
So at this instance it will advertise explicit label to upstream.
 
CASE-2 
Instance 1 :(At Ip router)  Admin has enabled LDP on IP router
interfaces also. At this instance, there is not chnage in network but
LDP session on interface connecting  LER2 and IP router is up.

Instance -2 : (At LER2) Internally the state m/c maintainence and
iteration implemenation should trigger the LABEL RELEASE TLV to the
upstream by LER2.
For this you can refer the state machine of LDP.

Instance -3: (At IP router) Ip router if configured of explicit mode
will now send a 'zero' label to LER2.
 
Note : As per RFC,  the instance of label release message and a new
label message sequence by LER2 dependend whether you are in control or
independent  mode . So instanse-2 and instance- 3 can flap.
 
Hope the flow is now unterstood by you.
 
P.S. Always post the query on mailing list.It may be helpful to
others.As Even at intial stage of my learning these types of question
from others helped me.
 
Regards,
Priyanka Gupta
Network Engineer

________________________________________________________________________
From: Vijaya Ramaraju <[email-masked]>
To: priyanka gupta <[email-masked]>
Sent: Monday, 10 August, 2009 9:06:47 AM
Subject: Re: Egress Router?

Thanks for your prompt reply priyanka !!!

yeah, I got it...

And my another doubt is 

   Scenario:    

  I have an LSP from LER1 to LER2 which is already established like
below and 
the LER2 will already be assigned with Label Zero(0) which is for Poping
up from that Node to IP  

IP0--------------->LER1---->LSRa------>LSRb----->LSRc---->LER2------------IP------------IP1                      
  la-12               la-13          la-14         la-15
la-0                                                             

Now the IP Router After the LER2 converted as MPLS Router...
which is nothing but the IP Router After the Current MPLS Egress is
Enabled as MPLS Router After certain period of the Existing MPLS LSP is
Established, like below.     

IP0--------------->LER1---->
LSRa------>LSRb----->LSRc---->LER2/LSR------------>LER------------>IP2 
la-12               la-13        la-14        la-15           la-0
la-0                                                

Now the New Edge is came into Picture and which is Edge Router for New
MPLS Domain and it will again Assign Zero(0)  Label for it,   
In this scenario the New Edge and the Previous Edge Both are having the
Zeros(0) as labels, which are in Improper manner Kindly suggest how to
proceed in this situation. 

=============--------------------------===============------------------------=================----------------------------------------========

Presently, our team is working on IP Multicasting Over MPLS Domain...I
did not get any proper documentation clearly like LDP, so please suggest
some of the rfc's/Drafts.

-----Original Message-----
From: priyanka gupta <[email-masked]>
To: [email-masked]
Cc: [email-masked]
Subject: Egress Router?
Date: Sun, 9 Aug 2009 08:19:00 +0530 (IST)
Mailer: YahooMailRC/1358.27 YahooMailWebService/0.7.289.15

Hi Vijaya,   Q : How can we find a router, if it is an Egress Router or
not...?

As you have stated the RFC line "FEC refers to the  LSR itself" , It
means the destination IP address of the session /LSP is the local IP
address either interface or loopback address of the router, than the
router is considered as the egress router for that session.   Secondly,
say already a LSP is established till Router-D and nexthop router is not
running any signalling protocol(LDP/RSVP-TE), but the data packet is
destined to the nexthop router to Router-D, then router-D will be
considered as egress router for that FEC.   A router can be egree for a
FEC and non-egress for other FEC.   Hope I had given answer to your
query.   Regards, Priyanka Gupta Network Engineer

Today's Topics:

Message: 1

Hi Team, 

2) The next hop router for the FEC is outside of the Label switching
Network... Means if the nexthop is

not in the MPLS domain or if it
nexthop is in the peer list.
Correct me if I am wrong. 

Thanks and Regards

Vijaya Rama Raju Jampana 
Mobile: 9492755564 

DISCLAIMER:

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