layer-3 bfd optimization proposals for enterprise and campus networks

Cisco Confidential© 2012 Cisco and/or its affiliates. All rights reserved. 1

Layer-3 BFD Optimization Proposals for Enterprise and Campus NetworksVikram Hosakote

Sr. Software Developer, NOSTG

Cisco Systems, Boxborough MA

11/27/2012

Cisco Confidential© 2012 Cisco and/or its affiliates. All rights reserved. 2

• BFD optimization proposals

• Network topology

• Asymmetric sub-interfaces (no echo)

• Asymmetric sub-interfaces (with echo)

• BFD sub-interface optimization limitations

• Restrictions for BFD echo per-link

• Group-id allocation scheme (RFC 7419)

Agenda

© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3

BFD Optimization proposalsCriteria Current State New Proposal

Supported interface types

Ethernet and port-channel Used to group sessions over sub-interfaces of physical ports, and bundles/ PC in logical mode

Fast session selection criteria

Session running on the sub-interface with the numerically lowest VLAN tag is elected the Fast session

First session coming up is chosen as the Fast session session

Asymmetric Fast session->Slow session logic

Sessions get slowed down when Fast session election becomes asymmetric on BFD peers

Fast layer-3 convergence

Support for IPv6 No Yes

Checkpoint calculations

Approximate Very accurate


Network Topology

Po1

LC-1S1, S3

LC-2S2

LC-1S1, S2, S3

Session Description Symmetric

S1(L->R & R->L) Fast session-Fast session

Y

S2(L->R) Fast session->Slow session

N

S2(R->L) Slow session->Fast session

N

S3 (L->R & R->L) Slow session-Slow session

Y


Asymmetric sub-interfaces (no echo)

Session Description Active min_rx Active min_tx Savings

S1(L->R & R->L) Fast session->Fast session

Configured min_rx Configured min_tx None


Configured min_rx Slow Timer due to peer negotiation

Medium (max 19 packets per session)


Slow Timer Configured min_tx

S3 (L->R & R->L) Slow session->Slow session

Slow Timer due to peer negotiation

High (max 39 packets per session)


Asymmetric sub-interfaces (with echo)

Session Description ActualMin_rx

active_min_tx

echoTx Savings

S1(L->R & R->L) Fast session->Fast session

SlowTimer

Configured min_tx

Fast session generates echo at max timer value.

None



active_min_tx is set to slow timer value.

Slow session generates echo packets at slowTimer.

High (max 39 packets per session)

S3 (L->R & R->L)

Slow session->Slow session


BFD sub-interface optimization limitations

• Sub-interfaces are normal Dot1Q VLAN interfaces on intermediate L2 switches.

• VLANs sharing the same L2 network grouped in different sub-interface groups to optimize BFD sessions.

BFD peer-

L

BFD Peer -

R

L2

L2

L2BFD

Peer - R

L2

L2

BFD peer-

L


Restrictions for BFD echo per-linkCategory Operation Scope Restriction

Echo Enable Physical interface or Port-channel interface

None

Disable Allowed

Enable Sub-interface of Physical interface or Port channel.

None

Disable Allowed

Port channel mode = per-link

Configure (Set mode to per-link)

Port-channel interface only None

Unconfigure (no bfd per-link)

None


Group-id allocation scheme (RFC 7419)

Range Used by Comments0 – 0xFFFF Fate-sharing configured by

userbfd fate-sharing <group-id>

0x10000 – MAX (except the range in the next row)

Used by internal group-ids assigned by sub-interface

Ethernet Ports:

Port Channels:

0x00FFFFFF – 0x01FFFFFF

Unused Bytes

AF_TYPE (2)

VDC(6) Type(8) Port(8) Slot(8)

AF_TYPE (2)

VDC(6) Type(8) Channel(16)


Q & A


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layer-3 bfd optimization proposals for enterprise and campus networks

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