Subject: [PWE3] Query on VCCV LSP Ping

From: "A.G.Suresh Babu (RND)" <[email-masked]>
Date: Wed, 12 Nov 2008 20:31:51 +0530

Hi all,

Earlier i had few queries on the VCCV LSP Ping. The query i had posted
and reply i had received is in the end of this mail. In continuation
of my understanding i have few more queries regarding the receive path
for VCCV LSP Ping.

1. I like to know the reply path/format for VCCV Control Channel Type
1 with LSP Ping Reply mode 2.

  If the VCCV Ping Echo Request is of the given format

  Ethernet Header, MPLS Header ( Outer-Label, Inner-Label), CW (
#0001 in the first nibble), IP/UDP Header, LSP Payload with Reply mode
as 2.

  Will the VCCV PING Reply will be in the given below format

  Ethernet Header, MPLS Header ( Outer-Label, Inner-Label with TTL as
2), CW ( #0001 in the first nibble), IP/UDP Header, LSP Payload

  or the VCCV Ping Reply will be IP packet using the LSP Path

  Ethernet Header, MPLS Header ( Outer-Label) IP/UDP Header, LSP Payload

2. I like to know the reply path/format for VCCV Control Channel Type
1 with LSP Ping Reply mode 3.

 If the VCCV Ping Echo Request is of the given format

  Ethernet Header, MPLS Header ( Outer-Label, Inner-Label), CW ( #0001
in the first nibble), IP/UDP Header, LSP Payload with Reply mode as 2.

  Will the VCCV PING Reply will be in the given below format

  Ethernet Header, MPLS Header ( Outer-Label, Inner-Label with TTL as
2), CW ( #0001 in the first nibble), IP/UDP Header with Router alert
option set, LSP Payload

  or the VCCV Ping Reply will be IP packet in the LSP Path

  Ethernet Header, MPLS Header ( Outer-Label) IP/UDP Header with
Router alert option set, LSP Payload

3. I like to know the reply path/format for VCCV Control Channel Type
1 with LSP Ping Reply mode 4.

 If the VCCV Ping Echo Request is of the given format

  Ethernet Header, MPLS Header ( Outer-Label, Inner-Label), CW ( #0001
in the first nibble), IP/UDP Header, LSP Payload with Reply mode as 2.

  Will the VCCV PING Reply will be in the given below format

  Ethernet Header, MPLS Header ( Outer-Label, Inner-Label with TTL as
2), CW ( #0001 in the first nibble), IP/UDP Header with Router alert
option set, LSP Payload

  or the VCCV Ping Reply will be IP packet in the LSP Path

  Ethernet Header, MPLS Header ( Outer-Label) IP/UDP Header with
Router Alert set,  LSP Payload

4. Does LSP Ping Reply mode 4 should be only used for VCCV LSP Ping
i.e., Reply mode 2 and Reply mode 3 should not used for VCCV LSP Ping

5. Similarly I like to know the reply path/format for VCCV Control
Channel Type-2/Type-3 with LSP Ping Reply mode 2 or 3 or 4.
  Does the reply path take LSP Path for VCCV Type 2/3 for reply modes 2 or 3 ?
  Does the reply path take the control channel path/PW path for VCCV
Type 2/3 only for reply mode 4 ?

Generally i want to know whether LSP Path is taken as reply path for
VCCV LSP Ping Echo request for VCCV Type-1,2,3 with Reply mode 2 or 3
and only for Reply mode 4 the reply path is the PW path or control
channel path ?

Is it mandatory to use Reply Mode 4 only for VCCV LSP Ping ?

Is the reply mode 4 implemented by other vendors so that
interoperability can be tested ? or Generally only reply 2 or 3 is
used for VCCV LSP Ping and reply path taken in LSP Path.

Does as per RFC the control channel types packet format is only used
on the transmit path ?

Though the mail is a long mail, this will basically clear my doubts
which iam unable to understand from RFC 5085.

It will great if the authors of RFC 5085 can reply to this query.

Thanks
suresh

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

Suresh,

I think LSP Ping Echo reply can travel via IP path or MPLS Path. It
depends on the "Reply Mode" set in the MPLS Echo request.
But in the case of VCCV using LSP Ping the reply mode should be set to
4 (Reply via application level control channel"), so that the ping
replier will push the reply on to the MPLS Path using the proper label
stack.

Thanks
Phaniraj.

On Thu, Aug 7, 2008 at 3:36 PM, Suresh Babu Gajapathy <agsuresh
babu.gmail.com> wrote:

Hi everyone,

I have few queries on VCCV Ping.

1. What is the reverse path taken for VCCV Ping .

    i.e., Assuming VCCV Channel as Type -1 When LSP Ping Echo Request
are sent then it has 2 labels ( Tunnel Label, VC Label ) and Control
Word with payload as LSP Ping Request. What will the reverse path
taken. Will it be Tunnel Label, VC Label and Control word with LSP
Ping Reply payload or will it be IP Path ?

Thanks
suresh
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---

From: "Nitin Bahadur" <[email-masked]>
Date: Fri, 14 Nov 2008 11:34:26 -0800

> #0001 in the first nibble), IP/UDP Header, LSP Payload with 
> Reply mode as 2.
> 
>   Ethernet Header, MPLS Header ( Outer-Label, Inner-Label 
> with TTL as 2), CW ( #0001 in the first nibble), IP/UDP 
> Header, LSP Payload
> 

Reply mode 2:    Reply via an IPv4/IPv6 UDP packet

Reply can be sent as:

A) Plain IP packet: Ethernet header, IP/UDP header, payload
B) MPLS packet: Ethernet header, MPLS (outer-label), IP/UDP, payload
     This will happen if the return path to the ping-src is an LSP.
 
>   Ethernet Header, MPLS Header ( Outer-Label, Inner-Label), 
> CW ( #0001 in the first nibble), IP/UDP Header, LSP Payload 
> with Reply mode as 2.
> 
>   Ethernet Header, MPLS Header ( Outer-Label, Inner-Label 
> with TTL as 2), CW ( #0001 in the first nibble), IP/UDP 
> Header with Router alert option set, LSP Payload

Why do you need inner-label with TTL=2 ?
 
>   Ethernet Header, MPLS Header ( Outer-Label) IP/UDP Header 
> with Router alert option set, LSP Payload

Reply can be sent as:

A) Plain IP packet: Ethernet header, IP/UDP header with RA set, payload
B) MPLS packet: Ethernet header, MPLS (outer-label), IP/UDP with RA set,
payload
     This will happen if the return path to the ping-src is an LSP.

>   Ethernet Header, MPLS Header ( Outer-Label, Inner-Label), 
> CW ( #0001 in the first nibble), IP/UDP Header, LSP Payload 
> with Reply mode as 2.
> 
>   Ethernet Header, MPLS Header ( Outer-Label, Inner-Label 
> with TTL as 2), CW ( #0001 in the first nibble), IP/UDP 
> Header with Router alert option set, LSP Payload

It should be the above format, but you don't need the router-alert
option set.
Also, CW will be present only if CW has been negotiated.

>   Ethernet Header, MPLS Header ( Outer-Label) IP/UDP Header 
> with Router Alert set,  LSP Payload
> 
> 4. Does LSP Ping Reply mode 4 should be only used for VCCV 
> LSP Ping i.e., Reply mode 2 and Reply mode 3 should not used 
> for VCCV LSP Ping

There is no such restriction mentioned anywhere in the drafts. You can
use any mode 
for VCCV lsp ping replies. 

> 5. Similarly I like to know the reply path/format for VCCV 
> Control Channel Type-2/Type-3 with LSP Ping Reply mode 2 or 3 or 4.
>   Does the reply path take the control channel path/PW path 
> for VCCV Type 2/3 only for reply mode 4 ?
> 
> Generally i want to know whether LSP Path is taken as reply 
> path for VCCV LSP Ping Echo request for VCCV Type-1,2,3 with 
> Reply mode 2 or 3 and only for Reply mode 4 the reply path is 
> the PW path or control channel path ?
 
In general, you shouldn't be too concerned regarding how the reply path
will 
look like for every combination of reply-mode and VCCV-Type. You should
be concerned with making sure that you are able to handle each
reply-type.
If you can handle each reply-type (on source of ping), then it doesn't
matter 
what the VCCV type is.

> Is it mandatory to use Reply Mode 4 only for VCCV LSP Ping ?

Does the draft say so? If it does not, it is not mandatory.
 
> interoperability can be tested ? or Generally only reply 2 or 
> 3 is used for VCCV LSP Ping and reply path taken in LSP Path.

Please ask vendors or look up vendor product documentation.
 
> Does as per RFC the control channel types packet format is 
> only used on the transmit path ?

---

From: Sam Aldrin <[email-masked]>
Date: Fri, 14 Nov 2008 12:04:24 -0800

>   Ethernet Header, MPLS Header ( Outer-Label) IP/UDP Header, LSP  
Reply mode 2 means reply via ipv4/v6. If the default path back to  
source is MPLS, it will take MPLS lsp path.
> Router alert option set, LSP Payload
Same answer as above. MPLS path will be taken if the path back to  
source is via LSP.
> in the first nibble), IP/UDP Header, LSP Payload with Reply mode as 2.
I believe you mean to say reply mode above is 4.
> 2), CW ( #0001 in the first nibble), IP/UDP Header with Router alert
Why are you expecting TTL to be 2?
> Router Alert set,  LSP Payload
It will be the above. RA is not required to be set.
> i.e., Reply mode 2 and Reply mode 3 should not used for VCCV LSP Ping
Incorrect. RFC doesn't restrict you in that regd. In multi segment  
cases, reply via ip may not work in all the cases.
> and only for Reply mode 4 the reply path is the PW path or control
reply path is independent of CC type. As long as you support the  
reply path types, it doesn't matter which CC type the request arrived  
with.
> Is it mandatory to use Reply Mode 4 only for VCCV LSP Ping ?
No.
> used for VCCV LSP Ping and reply path taken in LSP Path.
reply mode is not provided for interoperability, rather how to get  
the reply back to source.
> Does as per RFC the control channel types packet format is only used
No.

-sam

---

From: Carlos Pignataro <[email-masked]>
Date: Sat, 15 Nov 2008 20:51:53 -0500

Hi Suresh,

Please find a couple of additional comments inline.

>      This will happen if the return path to the ping-src is an LSP.

With the Reply Mode of 3 (Reply via an IPv4/IPv6 UDP packet with Router
Alert), for the case "B" (MPLS Packet -- when the path back to the
source uses an LSP), there is an additional topmost MPLS Header with the
MPLS Router Alert label (MPLS RA Label == 1) (missing above).
This is from RFC 4379:
http://tools.ietf.org/html/rfc4379#section-4.5

4.5. Sending an MPLS Echo Reply
...
   If the Reply Mode in the echo request is "Reply via an
   IPv4 UDP packet with Router Alert", then the IP header MUST contain
   the Router Alert IP option.  If the reply is sent over an LSP, the
   topmost label MUST in this case be the Router Alert label (1) (see
   [LABEL-STACK]).

> If you can handle each reply-type (on source of ping), then it doesn't

I think this point above is key.

+ the reply mode is orthogonal to the CC Type, and only for reply mode
of 4 you should expect the reply over the VCCV channel.

This para might help as a general answer as well:

   Except in the case of Reply Mode 4, "Reply via application level
   control channel", echo replies are always sent in the context of the
   IP/MPLS network.

Thanks,

--Carlos.

-- 
--Carlos Pignataro.
Escalation RTP - cisco Systems
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