MPLS Label Stack Operations in Networks with MNA Incremental DeploymentBronze Dragon Consultingloa@pi.nuFuturewei Technologiesjames.n.guichard@futurewei.comFuturewei Technologieshaoyu.song@futurewei.comUniversity of Surreystewart.bryant@gmail.comMPLS Working Group
MPLS Network Action (MNA) allows MPLS packet to carry instruction and data for in-network services and
functions in an MPLS network. This document describes the FEC-based optimized operations on
the MPLS label stack when the network is mixed with LSRs which are capable or incapable of
processing MNAs.
MPLS Network Actions (MNA) is used to
support actions for Label Switched Paths (LSPs) and/or MPLS packets
in addition to the normal forwarding.
provides the architectural framework for MNA and
provides the design requirements for MNA. MNA can support actions encoded within or below the label stack.
describes some further
architectural concepts for MNA.
This document provides the operating procedures for MNA-capable and
non-MNA-capable LSRs where MNA encoding are carried within or below
the MPLS label stack. We show that MNAs can be gradually
introduced into an existing MPLS network.
The capability to handle MNAs is announced throughout the MPLS network, and
LSRs that do not understand this information simply ignore it.
The MNAs are carried below the top label and the presence
of MNAs are indicated by a bSPL in the label stack.
The MNA use cases can be found in .
A post-stack extension header may for example be used when it is required that
the packet carry a large instruction header and/or metadata for an MNA
.
Only MNA capable LSRs will process MNAs, LSRs that are non-MNA-capable will ignore
the MNA and forward the packet as if the information was not there.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 when, and only when,
they appear in all capitals, as shown here.
This document provides a set of examples to show the operations performed
on MPLS encapsulated packets in a network where MPLS MNAs are used. The
document does also illustrated the
procedures for processing of the information carried within the MPLS label
stack to indicate the presence of MNAs below the top label.
Assume a physical topology that includes both MNA capable LSRs and non-MNA
capable LSRs. The topology is intentionally kept quite simple.
LDP Downstream on Demand (DoD) or Downstream Unsolicited (DU), RSVP-TE,
an IGP or a centralized controller could be used to create the label
mappings between the LSRs in an MNA capable network. Referring to Figure 1,
and using LDP DU for illustration, creation of an MNA path used by A to send
MPLS encapsulated packets with MNAs to F is as show below.
For prefix F reachable at LSR F:
F advertises labels F:[ldp: implicit-null, MNA-FEC: implicit-null] to E
E advertises labels F:[ldp: 101, MNA-FEC: 201] to D
D advertises label F:[ldp: 102] to c
c advertises label F:[ldp: 103] to b
b advertises label F:[ldp: 104] to A
This will result in installed labels as shown in .
This section provides examples of forwarding for some common scenarios in
networks with a mix of MNA-capable and non-MNA-capable LSRs and packets with and
without MNAs encoded.
The examples assume the use of post-stack extension headers. The process is equally applicable
to in-stack MNAs.
For non-VPN there are two variants, either the MNA is present or it is not.
A sends packet to b
stack = [104, bSPL, HEH, EH, IP]
b is a legacy router so just swaps [104] to [103], and sends the packet to c
stack = [103, bSPL, HEH, EH, IP]
c is a legacy router so just swaps [103] to [102], and sends the packet to D
stack = [102, bSPL, HEH, EH, IP]
D is an MNA capable LSR and receives the packet with [102] on top of the stack;
D scans the packet for an MNA; D finds the MNA and processes it and then swaps the top
label
to [101] and then sends the packet on to E
Note: this goes on the standard FEC because we only announce in the packet
there is NO MNA. In this case MNA is present.
stack = [101, bSPL, HEH, EH, IP]
E receives [101] and scans the packet for MNA; it finds the MNA and processes it and then
pops the top label and send the packet to F
stack = [bSPL, HEH, EH, IP]
Note: E is the penultimate hop router so it pops the standard LDP label, and
send on the standard FEC to F.
F receives the packet and scans the packet for MNA; it finds the MNA and processes it.
As F is the ultimate hop it pops GAL, and removes bSPL, HEH and EH, processes IP
and forwards the packet.
In this example there is no MNA present in the packet.
A sends packet to b
stack = [104, IP]
b receives the packet, b is a legacy router so it just swaps [104] to [103] and
sends the packet to c
stack = [103, IP]
c receives the packet, c is a legacy router so it just swaps [103] to [102], and
sends the packet to D
stack = [102, IP]
D receives the packet. Since D is an MNA capable router, it searches the packet for
MNA but finds nothing, so D swaps [102] to [201], and
sends the packet to E
stack = [201, IP]
Note: in this case D sends the packet using the MNA-FEC as MNA is *not* present.
Note: If downstream is not MNA capable then D sends the packet on the standard FEC.
E receives the packet [201] and bypasses MNA searching and processing (received on the
"no MNA present" FEC; E is penultimate node so it pops MNA-FEC label; and
send the packet to F.
stack = [IP]; not exactly a "label stack", but listed here for symmetry
F receives [IP] and routes the packet
In these two examples there is VPN information in the label stack, in the
first there also MNAs in the packet.
A sends packet to b
stack = [104, VPN, bSPL, HEH, EH, IP]
b receives the packet; b is a legacy router and just swaps [104] to [103] and
sends the packet to c
stack = [103, VPN, bSPL, HEH, EH, IP]
c receives the packet; c is a legacy router and just swaps [103] to [102] and
sends the packet to D
stack = [102, VPN, bSPL, HEH, EH, IP]
D receives the packet; D is an MNA capable LSR; D will search the packet for
MNA and will find and process the MNA; D will then swap [102] to [101] and
sends the packet to E
stack = [101, VPN, bSPL, HEH, EH, IP]
Note: This packet will be sent normal IP standard FEC; only packets that does
not include any MNA will be sent on the "no MNA present" FEC.
E receives the packet; E is MNA capable LSR; E will search the packet for
MNA and will find and process the MNA; E will then pop [101] and
sends the packet to F
stack = [VPN, bSPL, HEH, EH, IP]
Note: E is penultimate hop so pops the LDP label and send the packet on normal
IP standard FEC; only packets that does not include any MNA will be sent on the
"no MNA present" FEC.
F receives and scans the packet for MNA; it finds an MNA and processes it.
As F is the ultimate hop it pops the bSPL and removes HEH and EH,
processes the VPN label and forwards the packet.
A sends packet to b
stack = [104, VPN, IP]
b receives the packet; b is a legacy router and just swaps [104] to [103] and
sends the packet to c
stack = [103, VPN, IP]
c receives the packet; c is a legacy router and just swaps [103] to [102] and
sends the packet to D
stack = [102, VPN, IP]
D receives the packet; D is MNA capable LSR; D will search the packet for
MNA; D will not find any MNA; D will then swap [102] to [201] and
sends the packet to E on the "no MNA present" FEC.
stack = [101, VPN, IP]
Note: This packet will be sent on the "no MNA pesent" FEC;
E receives the packet [201] and bypasses MNA processing (received
on the "no MNA present" FEC; E is the penultimate node so it pops MNA-
FEC label; and send the packet to F on the "no MNA present" FEC.
stack = [VPN, IP]
Note: E is penultimate hop so E pops the "no MNA present" label and send the
packet to F.
F receives and scans the packet for MNA; finds no MNA and bypasses MNA processing.
As F is the ultimate hop it processes the VPN label and forwards the packet.
The RSVP-TE tunnel is not MNA capable or the capability has been disabled.
Assume a physical topology that includes both MNA capable LSRs and non-MNA
capable LSRs, as in the earlier examples. This topology also includes a low cost RSVP-TE tunnel between
b and D.
For this example the following assumptions are made:
An RSVP-TE tunnel has been established between b and D (packets will bypass c)
F is reachable at b through RSVP-TE tunnel
LDP is enabled on the RSVP-TE tunnel
For prefix [F]: The following label mappings are sent by the LSRs in the network.
F advertises labels F: [ldp: implicit-null, MNA-FEC: implicit-null] to E
E advertises labels F: [ldp: 101, MNA-FEC: 201] to D
D advertises label F: [ldp: 102] to c and F:[ldp: 102] to b
c advertises label F: [ldp: 103] to b
b advertises label F: [ldp: 104] to A
This will result in label mappings like this.
To describe the label stack operations in this case the VPN label stack is
used, starting with the case where an MNA is present in the packet.
A sends packet to b
stack = [104, VPN, bSPL, HEH, EH, IP]
b receives the packet, since b is a legacy router it swaps [104] to [102],
the next-hop reachable through the RSVP-TE tunnel; push the ingress RSVP-TE
tunnel label and send it via the tunnel to the tunnel endpoint D
stack = [RSVP, 102, VPN, bSPL, HEH, EH, IP]
Intermediate tunnel LSRs will forward (swap) based on the RSVP-TE label.
D receives the packet, D will pop the last RSVP-TE label; since D is an MNA
capable router it will search the stack and find the MNA, after processing the
MNA it will swap [102] to [101], and send the packet to E over the normal FEC
stack = [101, VPN, bSPL, HEH, EH, IP]
Note: this will be forwarded on the standard FEC because since the MNA
is present in the packet, only packet without any MNA is forwarded on the
"no MNA present" FEC.
E receives the packet [101]; since E is an MNA
capable router it will search the stack and find the MNA; after processing the
MNA it will pop [101], and send the packet to E over the normal FEC
stack = [VPN, bSPL, HEH, EH, IP]
Note: As E is the penultimate hop it will pop the standard LDP label.
F receives the packet with the VPN label on top [VPN]; E scans the packet for
MNA; it finds the MNA and processes it. As F is the ultimate hop it pops bSPL, and removes
HEH and EH, processes VPN label and forwards the packet.
A sends packet to b
stack = [104, VPN, IP]
b receives the packet [104]; be is legacy router and will not search for an MNA;
b swaps [104] to [102]; pushes [RSVP] sends packet to D over the RSVP-TE tunnel.
stack = [RSVP, 102, VPN, IP]
Intermediate tunnel LSRs will forward (swap) based on the RSVP-TE label.
D receives pops the tunnel label [RSVP], D is MNA capable and scans the packet
for MNA; D finds no MNA is present; pops RSVP-TE label, and then swaps LDP label
[102 ]to [201] and sends the packet to E
stack = [201, VPN, IP]
Note: in this case D sends the packet using the "no MNA present" FEC, since
there is no MNA in the packet.
Note: If the downstream LSR is not MNA capable then D will sends the packet
on the standard FEC.
E receives [201] and bypasses MNA processing since the packet is received on
the "no MNA present" FEC; E is the pen-ultimate hop so it pops the MNA-FEC label and
forward the packet to F
stack = [VPN, IP]
F receives the packet [VPN]; and scans the packet for MNA; it does not find any MNA, and it
processes VPN label and forwards the packet.
The case where an RSVP-TE tunnel is both MNA capable and MNA enabled is for
further study.
TBA
There are no requests for IANA actions in this document.
Note to the RFC Editor - this section can be removed before publication.
TBA
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