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IPv6 技術理論與實務研習班
IPv6 Routing
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Content
Routing Basic
Routing Protocols
IPv6 Routing Concept
RIPng for IPv6
Other IGP protocols for IPv6
Multiprotocols Extension for BGP-4
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Content
Routing Basic
Routing Protocols
IPv6 Routing Concept
RIPng for IPv6
Other IGP protocols for IPv6
Multiprotocols Extension for BGP-4
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Routing
Routing is the network layer function
Main issues in routing and flow control
–
–
–
–
throughput
average packet delay
throughput = offered load – rejected load
offered load may be rejected by the flow control
mechanism
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Delay requirement
Flow Control
Accepted traffic
(throughput)
Routing
Packets
Rejected
load
Network Performance
Measured
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The following examples illustrate the
performance (delay) affected by the routing
A good routing algorithm is to
–
–
Increase throughput
Decrease average delay
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Example 1
5 units
Paths (1, 3, 6)
(2, 5, 6) are better
than (1, 4, 6)
and (2, 4, 6)
5 units
2
1
4
All links have
A capacity of
10 units
5
3
6
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Example 2
5 units
15 units
2
1
4
All links have
A capacity of
10 units
5
3
6
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Classifications of Routing
Protocols
Route change – static routing v.s. adaptive
routing
–
–
Static routing: the path used by the sessions of each
origination-destination pair is fixed regardless of
traffic condition.
Adaptive routing: Paths change occasionally in
response to congestion.
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Routing and Flooding
Flooding and broadcasting
–
–
不將收到之packet回送給來源端
不重覆送出相同之packet
Shortest path routing
–
–
Each communication link is assigned a positive
number (called length), the length may be any
measurement criteria
Shortest path Min-hop (if the length of each
link=1)
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Introduction to Graph
A Graph G is defined as (N, A), where N is a
set of nodes, and a collection A of pairs of
distinct nodes from N
Spanning tree
Minimum weight spanning tree
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Importance of the Spanning
tree
A spanning tree is a subset of a network graph
that includes all nodes
There is only one path existed from the root
node to each leaf node
Reverse path forwarding
Minimum Spanning tree
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Considerations of Network
Routing
The length (weight) of each link (arc) may be
measured by delay, cost, performance, … etc.
Each node collects the network status (path
information) to calculate the shortest path to
destinations
Each node shall broadcast its link information
Flooding is necessary
Each node decides the shortest path from its
view point short path algorithms
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Content
Routing Basic
Routing Protocols Overview
IPv6 Routing Concept
RIPng for IPv6
Other IGP protocols for IPv6
Multiprotocols Extension for BGP-4
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IP Networks and Routing
Interior Routing Protocols
–
–
–
RIP (Routing Information Protocol)
OSPF (Open Shortest Path First)
Other Protocols
Exterior Routing Protocols
–
BGP (Border Gateway Protocol)
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RIP
RIP is a simple protocol based on distance vector
Overview of distance vector routing
–
–
–
–
Start up
Link breaks
Bouncing effect
Counting to infinity
Improvement schemes split horizon; triggered
updates
–
Decrease the time to converge
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Distance Vector
D
C
B
A
Routing
Table
Routing
Table
Routing
Table
Routing
Table
Pass copies of routing table to neighbors
periodically
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Distance Vector
10.1.0.0
10.2.0.0
10.3.0.0
A
B
C
Routing Table
Routing Table
Routing Table
10.1.0.0
0
10.2.0.0
0
10.3.0.0
0
10.2.0.0
0
10.3.0.0
0
10.4.0.0
0
10.3.0.0
1
10.4.0.0
1
10.2.0.0
1
10.4.0.0
2
10.1.0.0
1
10.1.0.0
2
•Routers build the best path to destinations
based on information from each neighbor
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Distance Vector
Process to
update this
routing
table
B
Process to
update this
routing
table
Router A
sends out
updated
routing
table
A
Topology
change
causes
routing
table
update
Updates proceed step-by-step from router to router
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Comparison of RIPv1(rfc-1058,
1988) and RIPv2 (rfc-2453, 1998)
Subnet routing – support subnet mask
information
Authentication – simple password protection
defined in 2453, and MD5 is defined in rfc2082
Next hop indication
Multicasting – define IP class D address for
information advertisement.
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OSPF
distance vector routing
–
Link state routing protocols are based on the
“distributed map” concept
Changing information of the network is
achieved by flooding protocol
Main issue – to maintain a synchronized copy
of the link state database in all nodes of the
network secure map updates
Shortest path first Dijkstra algorithm
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Link-State Concept
A2
A3
Link-State Packets
A1
Topological
Database
Routing
Table
Dijkstra
Algorithm
Shortest Path First Tree
After initial flood, only small event-triggered
updates are passed to other routers
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Distance Vector Routing v.s.
Link-State Routing
Distance Vector
Link-State
Views net topology from
neighbor’s perspective
Gets common view of
entire network topology
Adds hops from router to
router
Calculates the shortest
path to other routers
Frequent, periodic updates:
slow convergence
Event-triggered updates:
faster convergence
Passes copies of routing
table to neighbor routers
Passes link-state routing
updates to other routers
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Why is a link state protocol better?
Fast, loopless convergency
Support of precise/multiple metrics
–
The largest throughput; the lowest delay; the lowest
cost; the best reliability; …
Support multiple paths to a destination
–
Traffic splitting
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Protocols within RIP and
OSPF
RIP
–
–
–
–
RIP packets are carried over UDP/IP with port 520
Packets are sent every 30 seconds, or faster when
triggered updates
If a route is not refreshed within 180 seconds (6x30),
the distance is set to infinity
Each entry (one route) of RIP message is encoded
over 20 bytes long (reservation part is used in
RIPv2 for authentication, and etc.)
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Protocols within RIP and
OSPF
OSPF
–
–
OSPF runs on top of of the IP layer with protocol
type 89
Composes of 3 subprotocols
Hello: for checking the operation of the link and elect the
designated/backup routers
Exchange: master/slave operation for exchange the routing
information in DB
Flooding: to maintain the synchronization of the two
databases
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Other Routing Protocols
Intermediate System to Intermediate System (IS-IS)
–
Defined by ISO in 1980s for DECnet (especially in the
Backbone) and many concepts of IS-IS were adopted by
OSPF
IGRP (Internet Group Management Protocol)
–
–
–
Similar to ICMP and is a proprietary protocol defined by Cisco
Distance vector family protocol
Composite metrics: delay (D), bandwidth (B), reliability (R),
load (L)
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Choosing Routing Protocols
Criteria
–
–
convergence time
Resource comsumption
–
–
–
IP address
Network Bandwidth – link-state is better
processing power and memory – distance-vector is better
Ability to deal with multiple paths to a destination
Scalability – link-state is better
open standard or a proprietary protocol.
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Choosing Routing Protocols
Protocol
RIP
OSPF
IGRP
EIGRP
Type
distancevector
linkstate
distancevector
distancevector
Convergence Time
slow
fast
slow
fast
VLSM
no
yes
no
yes
Bandwidth
Consumption
high
low
high
low
Resource Consumption
low
high
low
low
Multi-path Support
no a
yes
yes
yes
Scales Well
no
yes
yes
yes
Proprietary
no
no
yes
yes
Routers Non-IP
Protocols
no
no
no
yes
a Some vendors may support multiple paths in RIP.
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BGP
Used for carrying routing information between AS’s
Path vector protocol
Runs over TCP (port 179)
Conveys information about AS path topology
AS 1
AS 2
BGP
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AS-Path Topology
AS 200
AS 100
170.10.0.0/16
180.10.0.0/16
180.10.0.0/16 300 200 100
170.10.0.0/16 300 200
AS 300
AS 400
150.10.0.0/16
AS 500
180.10.0.0/16 300 200 100
170.10.0.0/16 300 200
150.10.0.0/16 300 400
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BGP4
RFC 1771
Intelligent route selection based
on most specific prefix and shortest
Autonomous System (AS) path
BGP version 4 is the current
de facto exterior routing protocol
in the Internet
BGP- 4 is required for CIDR
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BGP
BGP is run over TCP/IP (with port number 179)
–
TCP provides a reliable data transmission link (with fair
flow/congestion control), however,
–
–
–
–
Routing update packet to cure network congestion,…
Security issue (rfc-2385, 1998 – Protection of BGP Sessions
via TCP MD5 Signature Option”) Packet types of BGP
OPEN
UPDATE
NOTIFICATION
KEEPALIVE
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BGP
Initial exchange
–
–
Use OPEN packet to check the BGP version and the “hold
time” (the number of seconds used by the “keep alive
procedure”)
Use UPDATE packet to exchange (list of) “withdrawn routes”
and metrics information of each path
Updates
–
–
Loop protection
Stable – the path shall not oscillate too rapidly between
reachable and unreachable
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BGP
Keep alive
–
According to the “hold time” value, and the keep alive
messages will not exchanged for zero hold time.
Error Notifications
–
–
–
–
–
–
Message header error
OPEN message error
UPDATE message error
Hold time expired
Finite state machine error
Cease (terminate the association)
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Policy in BGP
The commercial networks will not necessarily agree to
freely relay third parties’ traffic
Route decision process
–
Evaluate the paths that have been learned from external
routers
Attributes
–
–
Describes the characteristics of a particular prefix
AS path, Next hop, Local preference, Multi-exit discriminator
(MED), ….
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Content
Routing Basic
Routing Protocols Overview
IPv6 Routing Concept
RIPng for IPv6
Other IGP protocols for IPv6
Multiprotocols Extension for BGP-4
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IPv6 Routing
As in IPv4, IPv6 has two families of routing protocols:
–
–
Interior Gateway Protocols (IGP) for inside autonomous
systems
Exterior Gateway Protocols (EGP) for peering between
autonomous systems
Same “longest-prefix match” routing as IPv4 CIDR
Straightforward changes to existing IPv4 routing
protocols to handle bigger addresses
– unicast: OSPF, RIP-II, IS-IS, BGP4+, …
– multicast: MOSPF, PIM, …
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IPv6 Routing Concept
The loopback address “0:0:0:0:0:0:0:1” is a
virtual interface shall not send outside of a
single interface.
Link-local address
–
–
Used on a single link for the purpose such as autoaddress configuration, neighbor discovery, or when
no routers are present.
Routers must not forward any packets with link-local
source or destination address to other links.
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IPv6 Routing Concept
Link-local
10
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1111111010
0
interface ID
Site-local
10
1111111011
38
0
16
subbetID
64
interface ID
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IPv6 Routing Concept
Site-local address
–
–
Used for addressing inside of a site without the
need for global prefix.
Routers must not forward ant packet with site-local
source or destination address outside of the site.
Global
Site-Local
Link-Local
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Content
Routing Basic
Routing Protocols OverviewIPv6 Routing
Concept
RIPng for IPv6
Other IGP protocols for IPv6
Multiprotocols Extension for BGP-4
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RIPng for IPv6
Based on RIPv2, supports split-horizon with
poisoned reverse
RFC2080
Most (if not all) IPv6 router implementations
support RIP IPv6
Most IPv6-enabled Unix OS have the IPv6-RIP
routed daemon available
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RIPng for IPv6
Protocol Suite :
Type : Application layer , interior gateway,
distance vector
Port : 521 ( UDP )
The destination prefix is the usual 128-bit , IPv6
address prefix stored as 16 octets in network byte
order
Packets are sent every 30 seconds , or faster when
triggered updates
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RIPng packet format
Command(1)
Version(1)
Must be zero(2)
Route Table Entry 1 (20)
……
Route Table Entry N (20)
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RIPng packet format
Command : 8 bits
Command
1
Request ：A request for the responding system to send
all or part of its routing table
2 Response：A message containing all or part of the sender’s
routing table.This message may be sent in
response to a request, or it may be an unsolicited
routing update generated by the sender
Version : 1 ; 8 bits
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Response Messages
A Response can be received for one of
several different reasons:
– response to specific query
– regular update (unsolicited response)
– triggered update caused by a route change
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Route Table Entry(RTE) format
IPv6 prefix (16)
Route tag (2)
IPv6 prefix : 16 bytes
Route tag
: 16 bits
Prefix len
: 8 bits
Metric
: 8 bits
Prefix len (1)
Metric (1)
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The next hop RTE
IPv6 next hop address (16)
Must be zero (2)
Must be zero(1)
0xFF
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Timers and Split Horizon
Two timers are associated with each route
–
–
Timeout timer
Garbage-collection time
Split horizon
–
Split horizon is an algorithm for avoiding problems
caused by including routes in updates sent to the
nodes from which they were learned.
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Content
Routing Basic
Routing Protocols Overview
RIPng for IPv6
Other IGP protocols for IPv6
Multiprotocols Extension for BGP-4
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OSPF for IPv6
Also known as OSPFv3
Important rewrite to remove IPv4 dependencies.
(RFC 2470)
protocol independent
–
–
–
–
OSPFv3 runs over a link, rather than a subnet
Link-local addresses are used
Uses IPv6 for transport
The important rewrite on the protocol has delayed the
implementations. This results in an important delay for the
deployment of IPv6 in large networks
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IS-IS for IPv6
IS-IS is the OSI IGP protocol. It is network protocol
independent
Compared to OSPF, IS-IS for IPv6 is easier to
implement and modify
– new type-length-values (TLV) were defined:
New protocol identifier for IPv6
Router vendors supporting IS-IS for IPv4 have or are
probably going to have an IPv6 version
–
IPv6 Reachability (with 128 bits prefix)
IPv6 Interface Address (with 128 bits)
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Content
Routing Basic
Routing Protocols Overview
RIPng for IPv6
Other IGP protocols for IPv6
Multiprotocols Extension for BGP-4
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BGP4+ for IPv6
Includes multiprotocol extensions for BGP, for
new address families (ex: IPv6, VPN, …)
IPv6 address family:
–
–
Use scoped addresses in the NEXT_HOP
NEXT_HOP and NLRI are expressed as IPv6
addresses and prefix
Most IPv6 router vendors support IPv6 BGP. It
has been used on the 6Bone since 1996
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Multiprotocol Extensions for BGP-4
It can carry routing information for multiple
Network Layer protocol
(e.g., IPv6 , IPX , etc…)
The extensions are backward compatible
– a router that supports the extensions can
interoperate with a router that doesn’t
support the extensions
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Multiprotocol Extensions for BGP-4
To provide backward compatibility,as well as to
simplify introduction of the multiprotocol
capabilities into BGP-4; two new attributes are
used:
Multiprotocol Reachable NLRI (MP_REACH_NLRI)
Multiprotocol Unreachable NLRI
(MP_UNREACH_NLRI)
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MP_REACH_NLRI (Type code 14)
This is an optional non-transitive attribute that
can be used for the following purposes:
o
o
to advertise a feasible route to a peer
to allow a given router to report some or all of the
Subnetwork Points of Attachment (SNPAs)
that exit within the local system
MP_REACH_NLRI (Type code 14)
Address Family Identifier ( 2 octets )
Subsequent Address Family Identifier ( 1 octet )
Length of Next Hop Network Address ( 1 octet )
Network Address of Next Hop ( variable )
Number of SNPAs ( 1 octet )
Length of first SNPA ( 1 octet )
First SNPA ( variable )
………
Length of Last SNPA ( 1 octet )
Last SNPA ( variable )
Network Layer Reachability Information ( variable )
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MP_UNREACH_NLRI (Type Code 15 )
Address Family Identifier ( 2 octets )
Subsequent Address Family Identifier ( 1 octet )
Withdrawn Routes ( variable )
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Network Layer Reachability
information(NLRI) encoding
The Network Layer Reachability information
is encoded as one or more 2-tuples of the form
<length，prefix>,whose fields are described below:
Length ( 1 octet )
Prefix ( variable )
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Network Layer Reachability
information(NLRI) encoding
The use and the meaning of these fields are as follows:
Length:
The Length in bits of the address prefix. A
length of zero indicates a prefix that matches all
(as specified by the address family) address (with
prefix , itself , of zero octets)
Prefix: The Prefix field contains address prefixes followed
by enough trailing bits to make the end of the fall on
an octet boundary
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Subsequent Address Family Identifier
1 – Network Layer Reachability Information
used for unicast forwarding
2 – Network Layer Reachability Information
used for multicast forwarding
3 – Network Layer Reachability Information
used for both unicast and multicast
forwarding
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Summary
All routing protocols are available for IPv6
No real difference in the mechanics
RIPv6 is based on RIP-2
OSPFv6 is a major rewrite
IS-ISv6 includes few changes
BGPv6 is based on Multiprotocol BGP
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