The MPLS WG Archive

["chetan kumar s" <chetan.kumar@wipro.com>]

On Mon, 14 May 2001, Haseeb Budhani wrote:

Hi,
	Please look at the embedded messages..

> I have a follow-up question: Suppose a session has two adjacencies, and
> the session is currently using the TCP connection adjA for LDP-specific
> data flow. If adjA goes down for some reason, should the session be

Not exactly, ideally maintenance of session and adjecencies are two
different tasks. But there exists a relation, "if there are no more
adjecencies, then session can not exist, and converse is not true". So
specific to ur question, when the adjA goes down, U can continue with the
session, there is absolutely no change of any sort. If the adjB also goes
down, then U may have the close the session..

> closed down and restarted using the second adjacency adjB that belongs
> to this session, or should the session do a hot-swap of sorts and just
> start using the second adjacency ?? This could be a a failover
> application for LDP, but I'm not really sure if this is what the RFC is
> talking about.
> 
> I'd appreciate your comments at your convenience.

Thanks
Chetan S

> 
> Thanks. :)
> 
> --
> Haseeb Budhani.
> 
> "Sharma, Prem" wrote:
> 
> > Hi,
> >
> >      -----Original Message-----
> >      From: Haseeb Budhani [mailto:haseeb@ipinfusion.com]
> >      Sent: Monday, May 14, 2001 2:47 PM
> >      To: mpls@UU.NET
> >      Subject: Multiple adjacencies per session.
> >      Hello folks,
> >
> >      I have a few simple questions pertaining to the existence of
> >      multiple adjacencies per session, which RFC3036 says can
> >      only happen for point-to-point links (2.5.5 : Maintianing
> >      Hello Adjacencies)
> >
> >      1. Does one "session" between two peers denote one TCP
> >      connection between the two ??
> >      [Prem Sharma] Yes. There's one TCP connection per session.
> >      Two adjacent routers may have many sessions (many label
> >      spaces, many LDP Ids) and as many no. of TCP connections.
> >
> >      2. If the answer to (1) is Yes, does this mean that for n
> >      adjacencies in a session, only one -- the primary --
> >      adjacency has an active TCP connection, which it uses to
> >      exchange LDP specific information, and the other n-1
> >      adjacencies remain "idle" ?
> >      [Prem Sharma] I would rather put it like this: A session can
> >      have multiple adjacencies under its control. The periodic
> >      flow of  "Hellos" indicate the liveness of the adjacencies.
> >      All the adjacencies under the session have the same LDP
> >      identifier and for a specific LDP identifier, a specific
> >      transport address is exposed to the peer [If the transport
> >      address is not carried in the "Hellos" then the source ip
> >      address of the UDP packet is used to establish TCP
> >      connection]. Peer uses this transport address to establish
> >      TCP connection. Once the TCP connection is established,
> >      periodic keep alives over the TCP connection (in case LDP
> >      messages are not transacted for some time) indicate the
> >      sanity of the TCP connection from the LDP's point of view.
> >      Adjacencies are not idle; periodic "Hellos" keep on flowing
> >      over them (UDP packets). Once the flow of "Hellos" over an
> >      adjacency ceases, the adjacency is assumed inactive. When
> >      the last adjacencies under the session goes down, the
> >      session is assumed to be inactive.
> >
> >      3. If the answer to (1) is No, is there a TCP connection set
> >      up for every adjacency, and is this TCP connection used to
> >      exchange LDP specific data ??
> >      [Prem Sharma] No, pls. see the previous response.
> >
> >      Please get back to me at your earliest convenience
> >      [Prem Sharma]
> >
> >      Hope it helps.
> >
> >      Prem
> >
> >      .
> >
> >      Thank. :)
> >
> >      --
> >      Haseeb Budhani.
> >
>