201901-SRv6.pdf

Technical Overview
Segment Routing v6
Jakub Horn
Technical Marketing Engineer
CCIE#7543

• SRH
draft-ietf-6man-segment-routing-header-14
• Network Programmability
draft-filsfils-spring-srv6-network-programming-05
• IGP
draft-bashandy-isis-srv6-extensions-03
• BGP
draft-dawra-idr-srv6-vpn-04
• DEMO
service chaining
•
Content

IPv6 SR Header
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Destination Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
• IPv6 header
• Next header field: Indicates what comes next

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 SR Header
• IPv6 header
• Next header field: 4 → IPv4
4

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. type-specific data .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 SR Header
• IPv6 header
• Next header field: 43 → Routing
• IPv6 Routing extension header
• Generic header format defined in RFC 2460
• Next Header: IPv4, TCP, UDP, …
• Hdr Ext Len: Any IPv6 device can skip this header
• Segments Left: Ignore extension header if equal to 0
• Specific data depends on Routing Type field:
• 0 Source Route (deprecated since 2007)
• 1 Nimrod (deprecated since 2009)
• 2 Mobility (RFC 6275)
• 3 RPL Source Route (RFC 6554)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
43

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| First Segment | Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. ... .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n-1] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 SR Header
• IPv6 header
• Next header field: 43 → Routing
• IPv6 Routing extension header
• Generic header format defined in RFC 2460
• Next Header: IPv4, TCP, UDP, …
• Hdr Ext Len: Any IPv6 device can skip this header
• Segments Left: Ignore extension header if equal to 0
• Specific data depends on Routing Type field:
• 0 Source Route (deprecated since 2007)
• 1 Nimrod (deprecated since 2009)
• 2 Mobility (RFC 6275)
• 3 RPL Source Route (RFC 6554)
• 4 Segment Routing (tentative)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4
43
RFC
2460
SR
specific

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Source Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| First Segment | Flags | Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[0] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. ... .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Segment List[n-1] (128 bits IPv6 address) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
// Optional Type Length Value objects (variable) //
// //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 SR Header
• Each segment is an IPv6 address
• Segments are encoded in reverse order
• Last segment index is 0
• First segment index is First Segment
• Active segment index is Segments Left
• Active Segment is copied in the
Destination Address field of the IP header
• Additional data can be stored in TLVs
• Security (HMAC), NFV metadata, …
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4
43
First Segment
@Segment List [First Segment]
Last Segment / Final Destination
@Segment List [0]
Active Segment
Active Segment
@Segment List [Segments Left]

Source Node
• Source node is SR-capable
• SR Header (SRH) is created with
• Segment list in reversed order of the path
• Segment List [ 0 ] is the LAST segment
• Segment List [ " − 1 ] is the FIRST segment
• Segments Left is set to " − 1
• First Segment is set to " − 1
• IP DA is set to the first segment
• Packet is send according to the IP DA
• Normal IPv6 forwarding
Version Traffic Class
Next = 43 Hop Limit
Payload Length
Source Address = A::
Destination Address = B::
Segment List [ 0 ] = D::
Segment List [ 1 ] = C::
Next Header Len= 6 Type = 4 SL = 2
First = 2 Flags RESERVED
IPv6
Hdr
Segment List [ 2 ] = B::
SR
Hdr
Payload
Flow Label
Flow Label
D
D::
A
A::
SR Hdr
IPv6 Hdr SA = A::, DA = B::
( D::, C::, B:: ) SL=2
Payload
B
B::
C
C::

Non-SR Transit Node
• Plain IPv6 forwarding
• Solely based on IPv6 DA
• No SRH inspection or update
D
D::
A
A::
SR Hdr
IPv6 Hdr SA = A::, DA = B::
( D::, C::, B:: ) SL=2
Payload
B
B::
C
C::

SR Segment Endpoints
• SR Endpoints: SR-capable nodes whose
address is in the IP DA
• SR Endpoints inspect the SRH and do:
• IF Segments Left > 0, THEN
• Decrement Segments Left ( -1 )
• Update DA with Segment List [ Segments Left ]
• Forward according to the new IP DA
Next = 43 Hop Limit
Payload Length
Destination Address = C::
IPv6
Hdr
SR
Hdr
Payload
Flow Label
Flow Label
D
D::
A
A::
B
B::
C
C::
SR Hdr
IPv6 Hdr SA = A::, DA = C::
( D::, C::, B:: ) SL=1
Payload

SR Segment Endpoints
• SR Endpoints: SR-capable nodes whose
address is in the IP DA
• SR Endpoints inspect the SRH and do:
• IF Segments Left > 0, THEN
• Decrement Segments Left ( -1 )
• Update DA with Segment List [ Segments Left ]
• Forward according to the new IP DA
• ELSE (Segments Left = 0)
• Remove the IP and SR header
• Process the payload:
• Inner IP: Lookup DA and forward
• TCP / UDP: Send to socket
• …
Next = 43 Hop Limit
Payload Length
Destination Address = D::
IPv6
Hdr
SR
Hdr
Payload
Flow Label
Flow Label
D
D::
A
A::
B
B::
C
C::
SR Hdr
IPv6 Hdr SA = A::, DA = D::
( D::, C::, B:: ) SL=0
Payload
Standard IPv6 processing
The final destination does
not have to be SR-capable.

Segment format
• SRv6 SIDs are 128-bit addresses
• Locator: most significant bits are used to route the segment to its parent node
• Function: least significant bits identify the action to be performed on the parent node
• Argument [optional]: Last bits can be used as a local function argument
• Flexible bit-length allocation
• Segment format is local knowledge on the parent node
• SIDs have to be specifically enabled as such on their parent node
• A local address is not by default a local SID
• A local SID does not have to be associated with an interface
1111 : 2222 : 3333 : 4444 : 5555 : 6666 : 7777 : 8888
Locator Function

END – Default endpoint
• Default endpoint behavior (node segment)
• Decrement Segments Left, update DA
• Forward according to new DA
• Node B advertises prefix B::/64 (B::/64 is the SID locator)
• Packets are forwarded to B along the default routes (shortest path)
• On B, the default endpoint behavior is associated with ID 0 (0 is the function)
• The SID corresponding to the default endpoint behavior on node B is B::1
SR Hdr
IPv6 Hdr SA = A::, DA = B::0
(…,C::,B::1,…) SL=k
Payload
B
B:: /64
SR Hdr
IPv6 Hdr SA = A::, DA = C::
(…,C::,B::1,…) SL=k-1
Payload
C

END.X – Endpoint then Xconnect
• Endpoint xconnect behavior (adjacency segment)
• Decrement Segments Left, update DA
• Forward on the interface associated with the Xconnect segment
• Node C advertises prefix C::/64
• Packets are forwarded to C along the default routes (shortest path)
• On C, the endpoint xconnect behavior for link (C, E) is associated with ID CE
• The SID corresponding to endpoint xconnect-(C,E) behavior on node C is C::CE
SR Hdr
IPv6 Hdr SA = A::, DA = C::C1
(…,D::, C::C1,…) SL=k
Payload
SR Hdr
IPv6 Hdr SA = A::, DA = D::
(…,D::,C::C1,…)SL=k-1
Payload
C
C:: /64
D
1
2

Functoins Defined in Net Programming
• End Endpoint function The SRv6 instantiation of a prefix SID
• End.X Endpoint function with Layer-3 cross-connect The SRv6 instantiation of a Adj SID
• End.T Endpoint function with specific IPv6 table lookup
• End.DX2 Endpoint with decapsulation and Layer-2 cross-connect L2VPN use-case
• End.DX2V Endpoint with decapsulation and VLAN L2 table lookup EVPN Flexible cross-connect use-cases
• End.DT2U Endpoint with decaps and unicast MAC L2 table lookup EVPN Bridging unicast use-cases
• End.DT2M Endpoint with decapsulation and L2 table flooding EVPN Bridging BUM use-cases with ESI filtering
• End.DX6 Endpoint with decapsulation and IPv6 cross-connect IPv6 L3VPN use (equivalent of a per-CE VPN label)
• End.DX4 Endpoint with decapsulation and IPv4 cross-connect IPv4 L3VPN use (equivalent of a per-CE VPN label)
• End.DT6 Endpoint with decapsulation and IPv6 table lookup IPv6 L3VPN use (equivalent of a per-VRF VPN label)
• End.DT4 Endpoint with decapsulation and IPv4 table lookup IPv4 L3VPN use (equivalent of a per-VRF VPN label)
• End.DT46 Endpoint with decapsulation and IP table lookup IP L3VPN use (equivalent of a per-VRF VPN label)
• End.B6 Endpoint bound to an SRv6 policy SRv6 instantiation of a Binding SID
• End.B6.Encaps Endpoint bound to an SRv6 encapsulation Policy SRv6 instantiation of a Binding SID
• End.BM Endpoint bound to an SR-MPLS Policy SRv6/SR-MPLS instantiation of a Binding SID
• End.S Endpoint in search of a target in table T
• T.Insert Transit behavior with insertion of an SRv6 policy
• T.Insert.Red Transit behavior with reduced insert of an SRv6 policy
• T.Encaps Transit behavior with encapsulation in an SRv6 policy
• T.Encaps.Red Transit behavior with reduced encaps in an SRv6 policy
• T.Encaps.L2 T.Encaps behavior of the received L2 frame
• T.Encaps.L2.Red Transit with reduce encaps of received L2 frame

SRv6 for anything
Optimized for HW processing
e.g. Underlay & Tenant use-cases
Optimized for SW processing
e.g. NFV, Container, Micro-Service
Metadata TLV
Segments Left
Locator 1 Function 1
TAG

ISIS easily extensible
• Uses TLVs
• For Srv6:
• Locator – for Reachability (twice for backward compatibility)
• END function - TI-LFA and TE
• END.X function for each interface in routing protocol TI-LFA
and TE
• Capabilities:
• Max SID depth for different functions
• OSPF will follow
Ten0/0/0/0
Lo0
A::1/128
2001::12/64
Locator : B::/64
END: B::1
END.X: B::41
Ten0/0/0/1
END.X: B::42
fe80::dead/64
Router 1

VPNv4 – Basic SRv6 VPN –Control Plane
1 2
5
A2::A2
A1::A1
eBGP
AFI:1 -IPv4
SAFI:1
NLRI:4.0.0.0/8
NH:4.4.4.1
eBGP
AFI:1 -IPv4
SAFI:1
NLRI:4.0.0.0/8
NH:.3.3.3.2
A2::C4
end.DX4
A1::C3
end.DX4
3
3.0.0.0/8
3.3.3.1
3.3.3.2
4 4.0.0.0/8
4.4.4.1
4.4.4.2
iBGP
AFI:1 -IPv4
SAFI:128
NLRI:4.0.0.0/8
NH:A2::A2
Label:ImplNull
SID: A2::C4
A2::/64
IGP
A1::/64
IGP

VPNv4 – Basic SRv6 VPN -Data Plane
1 2 4 4.0.0.0/8
3
3.0.0.0/8
5
A2::A2
A1::A1
A2::C4
end.DX4
A1::C3
end.DX4
3.3.3.1
3.3.3.2
4.4.4.1
4.4.4.2
IPv4 ( 3.1.1.1, 4.1.1.1)
payload
IPv6 ( A1::1, A2::C4 )
payload
IPv4 ( 3.1.1.1, 4.1.1.1)
IPv4 ( 3.1.1.1, 4.1.1.1) )
payload

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Segment Routing, Part I - Textbook

1
5
2
3
eMBB Service
4
NCS540
NCS540
NCS5500
NCS5500
NCS540
APP
NSO
gNB
UPF
SRv6
DC-NFV

1
5
2
3
URLLC Service
4
NCS540
NCS540
NCS5500
NCS5500
NCS540
APP
NSO
gNB
UPF
SRv6
DC-NFV
Type:4(SRH)
NH:IPv4|SL:1
Segment List:
[0]:2001:0:0:8:89::A
[1]:2001:0:0:4::1
SA:2001::7
DA:2001:0:0:4::1
NH:SRH
SA:10.1.1.1
DA:10.2.2.2
Protocol:TCP
TCP Header/Data

1
5
2
3
Service Chaining
4
NCS540
NCS540
NCS5500
NCS5500
NCS540
APP
NSO
gN
B
UP
F
SRv6
DC-NFV
QOS DPI FW IPS

201901-SRv6.pdf

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