FRR Facility Link and Node Protection

Generally the MPLS are used to transmit the L2 traffic, for which it has 3 labels, the transport label, the VC label and the PLR adds one more label which is known as bypass label.

So after the PLR reroutes the traffic it has 3 labels the outer bypass label, the transport label and the VC label.

FRR Node protection:-

Facility Backup

In tihs case all the protected LSP 's in the same network segment share the same bypass tunnel.

Facility bypass reduces the number of bypass tunnels required to provide protection to the main LSP

Facility bypass tunnel cannot be used as a backup for those LSP which are configured with a reservation style of FF.

When a failure of a link occurs traffic from multiple LSP;s are rerouted by the PLR through the same bypass tunnel.

When the traffic reaches the MP router it merges the traffic back to the primary LSP, in order to achieve this purpose the MP router must be aware of the LSP's in which each flow belongs to. Favility bypass tunnel takes advantage of the MPLS label stack and uses a third label to encapsulate  the protected traffic and carry it through the bypass tunnels.

The following is seen when facility backup is used:-

When the PLR reroutes the traffi c away from the local failure, it keeps both
labels in the protected traffi c’s MPLS label stack. It pushes the third bypass
tunnel label to re-encapsulate the protected traffi c and then sends the traffi c over
the bypass tunnel. The protected traffi c now has one more label in the MPLS
label stack, the bypass tunnel label on the top.
• All routers along the bypass tunnel swap only the top bypass tunnel label to
switch the traffi c toward the termination point of the tunnel. The protected
traffi c is tunneled from the PLR to the MP router; this is why the protection tunnel
used by FRR facility backup is called the bypass tunnel.
• At the termination point of the bypass tunnel, the MP router fi rst pops the
bypass tunnel label to expose the original traffi c. Then, the MP identifi es the
original LSP-Path by examining the outer labels (MPLS transport label) and
merges the traffi c back to the correct protected LSPs.

The bypass tunnel is used for a multiple LSP hence each of them uses its own tunnel-id and LSP-id.

The

facility bypass uses the Near-MP approach:

• For link protection, the bypass tunnel originates at the PLR and terminates at

the PLR’s NHop router. The MP is always the NHop router of the PLR.

• For node protection, the bypass tunnel originates at the PLR and terminates at

the PLR’s NNHop router. The MP is always the NNHop router of the PLR.

Thus, LSP-Paths can share the bypass tunnel providing their paths go through

same PLR and MP.

When an HE router has an LSP confi gured with facility backup desired, the HE

router sends a PATH message indicating this by:

• Adding the

set (

• Setting the

FAST_REROUTE object having the facility backup desired fl ag0x02)SESSION_ATTRIBUTE object’s fl ag of local-protection-desired

bit to 1. If node protection is desired, it will also set the

node-protection-desired

not have a fl ag indicating node protectionbit to 1. The FAST_REROUTE object does
Once it receives the path message from the HE router all the routers assume the PLR role and start to establish bypass tunnels

The path message of each of the PLR when they assumed the role of the PLR has the following items:-

Fast Reroute object:- This contains the ip address of the PLR and the ip address the detour LSP  is trying to avoid.

In the

format of

As an example, the bypass tunnel name of

this tunnel is providing a link protection for the link with one side’s IP address 10.117.118.1. All LSPs desiring link protection on that link, by that particular
IP address, can share this tunnel.

Once established the bypass tunnel becomes a common facility and can be used by many LSP traversing the path hence the name bypass.

SESSION_ATTRIBUTE object, the name of the bypass tunnel is set to thebypass-{link|node}{IP address of the protected object}.bypass-link10.117.118.1 means that

Detour Merge Point

Detour Merge Point is the router where multiple detour LSP intersect and merge.

Merging one to one detour tunnels reduces the number of LSP in the entire network.

One to One backup

One to one backup has better granularity then facility however it uses more resources.

In one to one backup each LSP has its own detour LSP in one to one backup policy although it requires more granularity but it consumes more resources.

The HE router sends a path message with the one to one desired flag set.

If the node protection is desired the session attribute flag also has the node protection desired flag set.

After the FRR is established all the routers except the tail router assumes the role of PLR and creates a detour path.

The detour LSP has the same tunnel-id and LSP-id as the primary LSP

They all have a Detour object containing the PLR router ip address and the ip address that the detour LSP is trying to avoid.

All the detour LSP have the following naming conventions Protected LSP name::Protected LSP path name_detour.

lsp-to-163::163_detour means that this detourlsp-to-163 and path name 163.

 

 

If  a primary LSP traverses n hops in the network then there will be n-1 LSP's in there network, although no detour configuration is necessary however in a highly scalable network this increases the number of LSP to a huge number.

 

The PLR notifies the HE router of the failure by setting the local-repair-in-use flag set in the path error message.

 

 

When there is a failure the PLR tries to establish node protection with 3 attempts if node protection is not possible then the router resorts to link protection.

 

First the primary LSP is set up by exchanging the labels

 

When the PLR signals the detour LSP to the merge point, the merge point distributes labels for the detour LSP and also It  programs to swap the label 200 with label 100 if the detour LSP is used.

 

 

 

Merge Point

This is the point where the protection tunnel and the protected LSP meets. This is also the tail end router of the protection tunnel.

The functions of Merge point includes  merging the trafic back to the protected LSP path.

Maintain the protection tunnel state:-  RESV messages are sent to refresh the protection tunnel.

Location of the Merge Point:-

Far MP approach:- In this case the MP terminates as close as possible to the Tail end router

Near MP approach:- In this case the MP terminates very near to the PLR, for link protection it terminates to the next hop router and in the case of Node protection it terminates to next to next hop router.

One to One uses the far MP approach and the facility implements near MP approach.

Point of Local Repair

When FRR is configured all the routers along the path assumes the role of the PLR

The label used by the PLR when there is a failure ie for the detour path depends upon the type of FRR which is being used. In the case of one to one the label used for the detour path is the label which is being assigned by the immediate downstream router on the detour path.

In the case of facility backup the data from the protected LSP is tunneled across a bypass tunnel, hence the outer label is the label which is assigned by the immediate downstream router of the detour path the PLR also has to know the label which is being expected by the Merge point, the record label option makes this possible for the RRO. Hence the PLR adds two labels one which is being received from the immediate downstream router of the detour path, the second label is the label which the Merge point expects.

Two messages are sent by PLR towards the HE router notifying the failure

Path Error message:- RSVP notify error and the value is tunnel locally repaired

It also sends the FRR in use flag set in the RRO object of the RESV message.

Head End Router

This is the origination point of the LSP. The head end router informs if one to one or facility is desired in the path message session attribute object. After each router along the lsp path receives the path message it acts as a PLR and tries to set up the detour, each PLR informs the HE router if the detour is available or not.

PLR informs the HE router of a failure in 2 ways:-

1> It sends the RESV message to the HE router where the local protection in use flag is set.

2> PathErr message with an ERROR object. The error0x19) — RSVP Notify Error. The error value is0x03) — tunnel locally repaired.

The PLR sends a

code is 25 (

3 (

Once a path error is receivd by the HE router it switches the traffic to a secondary standby LSP, if a standby LSP is not available it tries to initiate a LSP in an Make Before Break (MBB) manner.

When the HE router comes to know that a FRR is in use it starts the MBB process immediately however it initiates the process of establishing the LSP after some time ie after the retry timer expires.

After the MBB process is successful traffic is switched immediately to the standby LSP.

General FRR End to End

1.

request for protection. Each router along the path of the LSP records the

route and label for the HE router.

If protection is desired in an LSP, the RSVP-TE signals the LSP with a

2.

by sending an RESV message back. The FRR is established only after

the protected LSP-Path comes

each router does not start the signaling or protection tunnels. The RESV

message from P6 for the initial LSP path establishment does not report

whether the local protection is available yet.

After the PATH message reaches the Tail router P6, P6 establishes the LSPPathup operationally. Therefore, at this moment,

3.

Then, the CSPF in each router starts calculating the detour LSP or

bypass tunnel based on the network topology stored in the TED, and the

original path of the LSP recorded in the RRO object by each hop.

After the initial RESV reaches the P1 router, the protected LSP is established.

4.

the CSPF calculation. If the detour LSP or bypass tunnel is established, the

router then announces the protection availability to the HE router.

Each potential PLR router signals the detour LSP or bypass tunnel based on

5.

protection are available from which router.

When a failure happens, the PLR immediately uses the pre-signaled protection

to reroute the traffi c around the failure and notifi es the HE router via

the At this point, the HE router of the protected LSP has a view of what types ofPathErr message and the RESV message.

Network Elements in FRR

Head End Router:-  The head end router sets the local protection desired flag in the path message, it might also set the node protection desired flag also in the path message depending link protection or node protection is desired.

During network failure when the headend router receives the Path error message it tries to optimize the LSP or find a new path for the lsp, depending on the mode used global revertive mode.

Point of Local repair:- This creates a detour for the LSP that needs to be protected. It sends a path error message to the HE router if the detour is in use with the local repair in use flag set.
It also responds to the path message from the HE router by sending a RESV message to the HE router by setting the local protection available flag set.

Merge Point :- The point where the protected LSP and the protecting tunnel meet.  The MP merges the traffic back from the protecting tunnel to the original LSP. In link protection MP is next hop and in the case of node protection the MP is NNHOP.

RSVP-TE for FRR

The FRR protection tunnel LSP’s set-up priority, holding priority, hoplimit,

and bandwidth (bytes per second)

• Protection method: one-to-one (

• Administrative group (link-coloring) information such as

0x1) or facility (0x2)include-any,

exclude-any

32-bit masking, mapping to the 32-bit admin group bits

New

messages for one-to-one backup only. It contains a list of possible PLRs and the

node each PLR should avoid.


FRR-Related Flags Defi ned in the SESSION_ATTRIBUTE Object — In
the PATH message, the SESSON_ATTRIBUTE object has an 8-bit fl ag fi eld.
In the RSVP-TE for MPLS LSP signaling (RFC 3209), the fi rst three
least signifi cant bits are defi ned: local-protection-desired (0x1),
label-recording-desired (0x2), and SE-style-desired (0x4). RFC
4090 uses the next two bits for FRR: bandwidth-protection-desired (0x8)
and node-protection-desired (0x10). These two bits allow the HE router
to indicate the desire for node protection and the reservation of bandwidth
for the FRR protection tunnels.
• FRR-Related Flags Defi ned in the RRO Object — In the PATH and
RESV messages, the RRO object has an 8-bit fl ag fi eld in each IPv4
subobject. In the RSVP-TE for MPLS LSP signaling (RFC 3209), the fi rst
two least signifi cant bits are used: local-protection-available (0x1)
and local-protection-in-use (0x2). RFC 4090 uses the next two
bits for FRR: bandwidth-protection-available (0x8) and
node-protection-available (0x10). These two bits allow the Tail
router to indicate the availability of node protection and reservation
of bandwidth for the FRR protection tunnels.

DETOUR Object (Object Class 63) — This object is used in the PATH, and include-all subobjects. Each of these subobjects is a

Point of local Repair (PLR) & Merge Point

The router providing the failure protection is called the point of local repair (PLR).

During the failure the PLR sends the path err message to the HE router. The PLR should also notify the HE router that the FRR is in use.

When a PLR reroutes the traffic across the failure it sets the local protection in use flag in the RESV message which is sent back to the HE router.

The merge point (MP) is the router where the rerouted traffic merges back to the original path.

Every router along the LSP path should consider itself as a potential PLR except the Tail end router, also every router should consider itself as the merge point except the HE router.

Link Protection and Node protection

First the PLR desires node protection if the node protection is not possible then link protection is done.

FRR Protection Terminologies

Terminology Description

Protected LSP The LSP-Path being protected by FRR. This LSP-Path is the original

LSP-Path that requires protection. Only the primary LSP-Path in an LSP

can be protected by FRR.

Protection LSP The LSP-Path established by FRR to provide protection. The term

protection LSP-Path

facility backup bypass tunnel.

can refer to either a one-to-one detour LSP or a

Detour LSP The LSP-Path established by FRR to provide one-to-one backup to

certain LSP-Paths desiring protection

Bypass tunnel The LSP-Path established by FRR to provide facility protection to

certain LSP-Paths that traverse the same common facility

Fast Reroute

Requires traffic engineering extensions on OSPF.

Every hop creates one protection tunnel , when facility backup is implemented multiple LSP can be backed up by a single LSP.

When a failure occurs the router closest to the failure provides protection.

There are two methods of FRR protection:-

One-to-One Backup

LSP signaled that is dedicated to protect that LSP-Path. The one-to-one

backup that is signaled is called the

— Each LSP-Path desiring one-to-one backup has a protectiondetour LSP.

• Facility Backup

all LSP-Paths traversing a common facility path. Any LSP-Paths desiring FRR

protection share the common protection tunnel when their paths intersect.

This is a many-to-one protection relationship. The facility backup protection

signaled is called the

— Facility backup creates a common bypass tunnel to protectbypass tunnel.