Softwires Hub & Spoke using L2TPv3

Bill Storer

L2TPv3 (RFC 3931) Improvements

• Supports multiple encapsulations– UDP– IP (Protocol 115)

• Supports multiple payload types– PPP– IP

• Supports enhanced security– Message digest on every control message– Lightweight cookie on data messages

• L2TPv3 supports VCCV– Enhanced diagnostic and fault detection

Which improvements should we use?

• UDP vs IP encapsulation– UDP MUST be supported

• NAT– IP (Protocol 115) MUST be supported

• Stated in RFC• PPP vs IP payload

– PPP MUST be supported• Easiest to integrate with existing L2TPv2 support

– IP SHOULD be supported• Enhanced security

– Use of enhanced security is optional– MUST support message digest if requested– MUST support cookie if requested

• VCCV– MAY be supported as needed

Use of the IP Pseudowire

• Authentication may be provided using tunnel authentication– Host Name AVP is the user name– A shared secret is associated with the SI’s host

name on the SC– Host Name and shared secret may be provided to

the SI just as the PPP user name and password are provided

– Only one user per tunnel, which is standard for H&S

• PANA is also an option for Authentication– draft-ietf-pana-pana-12

Use of the IP Pseudowire (cont)

• IP address assignment– DHCP for IPv4– Stateless auto config and/or DHCPv6 for

IPv6– No new AVPs necessary

Use of the PPP Pseudowire

• PPP authentication may be used (same as L2TPv2)• Tunnel authentication as in the IP Pseudowire• IPv4 address assignment

– IPCP MUST be used for initial address assignment– DHCP MUST be used for prefix delegation

• IPv6 address assignment– IPv6CP MUST be used to determine the Interface ID portion

of the address– DHCPv6 or stateless autoconfig may be used for the prefix

portion of the address– DHCPv6 MUST be used for prefix delegation

L2TPv3 Message Details

SCCRQ Message

• MUST AVPs– Host Name

• May be used to authenticate end user• May be “Softwires” if no authentication

– Router ID• MUST NOT be sent for Softwires• Marked as MUST, but only for LAC-LAC applications.

– Pseudowire Capabilities List• IP, PPP, or both

– Others• As specified in the draft

• MAY AVPs– Control Connection Tie Breaker

• Should never be a tie– Others as needed

SCCRP Message

• MUST AVPs– Host Name

• May be used to authenticate end user• May be “Softwires” if no authentication

– Router ID• MUST NOT be sent for Softwires• Marked as MUST, but only for LAC-LAC applications.

– Pseudowire Capabilities List• IP, PPP, or both

– Others• As specified in the draft

• MAY AVPs– As needed

SCCCN and StopCCN Messages

• MUST AVPs– As specified in the draft

• MAY AVPs– As needed

HELLO Message

• We need the HELLO message– Don’t have any other keep alive message for IP

Pseudowire– Prefer to use the HELLO instead of the LCP echo

for PPP Pseudowire

• MUST AVPs– As specified in the draft

• MAY AVPs– As specified in the draft

ICRQ Message

• MUST AVPs– Pseudowire Type

• IP or PPP

– Remote End ID• MUST NOT be sent for Softwires• Marked as MUST, but only for LAC-LAC applications.

– Circuit Status• New and Active bits set

– Others• As specified in the draft

ICRQ Message (cont)

• MAY AVPs– Session Tie Breaker

• Should be no ties

– Data Sequencing• Shouldn’t be necessary

– Others• As specified in the draft

ICRP Message

• MUST AVPs– Circuit Status

• New and Active bits set

– Others• As specified in the draft

• MAY AVPs– Data Sequencing

• Shouldn’t be necessary

– Others• As specified in the draft

ICCN Message

• MUST AVPs– As specified in the draft

• MAY AVPs– Data Sequencing

• Shouldn’t be necessary

– Others• As specified in the draft

CDN Message

• MUST AVPs– As specified in the draft

• MAY AVPs– As needed

SLI and WEN Messages

• SLI is not relevant to softwires– Change in circuit status disconnects call– No special information needs to be sent

after the call is established

• WEN is not relevant to softwires– Softwires uses voluntary tunneling

Explicit Ack Message

• Necessary if using authentication

• MAY AVPs– As specified in the draft

PPP Payload Specifics

• draft-ietf-l2tpext-l2tp-ppp-xx.txt– Discusses transport of PPP over L2TPv3

• Forwarding PPP frames– Very similar to L2TPv2– Address and Control fields are NOT transmitted over

the tunnel

• Only one of the PPP specific AVPs discussed there has relevance to softwires

– Offset Size– Use is optional

IP Payload Specifics

• draft-ietf-l2tpext-pwe3-ip-xx.txt– Discusses transport of IP over L2TPv3– Not very relevant to Softwires– Needed to define the IP payload type