Chapter 16. Internetwork Operation Routing Protocols Integrated Services Architecture Resource Reservation: RSVP Differentiated Services

Protocols in the Chapter

Routing Protocols Autonomous systems (AS) An internet connected by homogeneous routers; generally, the routers are under the administrative control of a single entity Interior router protocol (IRP) Passes routing information between routers within an autonomous system Exterior router protocol (ERP) Passes routing information between routers in different autonomous systems

Routing Protocols (cont)

Hierarchical Routing Hosts Interior Gateways Exterior Gateways Maintain sufficient routing information to forward datagrams to other hosts or an interior gateway(s) that is (are) attached to the same network. (ARP) Interior Gateways Maintain sufficient routing information to forward datagrams to hosts or other interior gateways within the same autonomous system Exterior Gateways Maintain sufficient routing information to forward datagrams either to an interior gateway, if the datagram is for the same autonomous system, or to another exterior gateway, if it is not.

Border Gateway Protocol Standardized exterior router protocol for the Internet (BGP-4, RFC 1771) Allows routers (gateways) in different autonomous systems to cooperate in the exchange of routing information. Operates in terms of messages, which are sent over TCP connections. Message: Open, Update, Keepalive, Notification 3 functional procedures Neighbor acquisition, Neighbor reachability Network reachability (Routing update)

BGP (cont) Neighbor acquisition Neighbor acquisition occurs when two neighboring routers in different autonomous systems agree to regularly exchange routing information 1. One router sends an Open msg to another 2. If the target router accepts the request, it returns a Keepalive msg in response

BGP (cont)

BGP (cont) Neighbor reachability Network reachability Used to maintain the neighbor relationship Two routers periodically issue Keepalive msg to each other Network reachability Each router maintains a database of the subnetworks that it can reach and the preferred route for reaching that subnetwork Whenever a change is made to this database, the router issues an Update msg that is broadcast to all other routers implementing BGP

BGP (cont) For authentication

BGP (cont)

OSPF Protocol Open Shortest Path First Protocol Interior routing protocol by ARPANET Link-state routing algorithm Each router maintains descriptions of the state of its local links to subnetworks, and from time to time transmits updated state information to all of the routers of which it is aware Each router maintains a database that reflects the known topology of the autonomous system

OSPF Protocol (e.g.) Sample autonomous system

OSPF Protocol (e.g.) Directed graph of the sample autonomous system

OSPF Protocol (e.g.) SPF tree for router R6 Using Dijkstra’s Algorithm

OSPF Protocol (e.g.) Routing Table for router R6

ISA Concept Integrated Services Architecture Intended to provide QoS transport support over IP-based internets, RFC 1633 Two broad categories of traffic on internet Elastic Traffic File transfer (FTP) , Email (SMTP), Remote Logon (TELNET), Network management (SNMP), Web access (HTTP) Inelastic Traffic Real-time traffic Throughput, Delay, Jitter, Packet loss

ISA Approach Traditional (IP) Router mechanisms Routing algorithm Packet discard ISA Enhancements: the concept of flow Admission control: RSVP Routing algorithm: QoS-based OSPF Queuing discipline: For differing requirements of different flow Discard policy: for managing congestion and meeting QoS guarantees

ISA Components ISA Implemented in Router

2-Level ISA Services 1. General categories of service Guaranteed Assured capacity/data rate Specified upper bound on the queuing delay No queuing loss Controlled Load Best effort 2. Service for a particular flow Traffic specification (TSpec): Token Bucket QoS

Token Bucket Scheme

Queuing Discipline No priority; Larger mean delay Greedy TCP connections crowd out altruistic ones Weighted Fair Queuing (WFQ)

Resource ReSerVation Protocol Characteristics Unicast and Multicast Simplex Receiver-initiated reservation Maintaining soft state in the internet Providing different reservation styles Transparent operation through non-RSVP routers Support for IPv4 and IPv6 Type-of-Service in IPv4 Flow Label in IPv6

RSVP Design Characteristics Receiver-initiated reservation Sender Provide the routers with the traffic characteristics of the transmission (data rate, variability) Receiver Specify the desired QoS Router Aggregate multicast resource reservations for the shared path segments along the distribution tree Soft State

RSVP Data Flows Flow descriptor flowspec: desired QoS filterspec: defines the set of packets for the reservation Treatment of packets of one session at one router

RSVP Protocol Mechanisms Two message types Resv, Path

RSVP Operation

Differentiated Services (DS) Goal (RFC 2475) Provide a simple, easy-to-implement, low-overhead tool to support a range of network services (comparing with ISA) Key characteristics IP packets are labeled for differing QoS treatment using the existing IPv4 Type-of-Service octet or IPv6 Traffic Class octet. Thus, no change is required to IP

Differentiated Service (cont) A service level agreement (SLA) is established between the service provider (internet domain) and the customer prior to the use of DS All traffic with the same DS octet is treated the same by the network service Routers deal with each packet individually and do not have to save state information on packet flows

DS Octet Packets are labeled for service handling by means of the DS octet Placed in the Type of Service field of an IPv4 header, or the Traffic Class field of the IPv6 header RFC 2474: The leftmost 6 bits form a DS codepoint The DS codepoint is the DS label used to classify packets for differentiated services

DS Codepoint (6 bits) xxxxx0 xxxx11 xxxx01 Reserved for assignment as standards 000000: default packet class, i.e. best-effort xxx000: reserved to provide backward compatibility with the IPv4 precedence service xxxx11 Reserved for experimental or local use xxxx01 Reserved for experimental or local use, but may be allocated for future standards action as needed

DS Domain Within a domain, the interpretation of DS codepoints is uniform, consistent service is provided

Routers in DS Domain Interior nodes (per-hop behavior: PHB) Queuing discipline to give preferential treatment depending on codepoint value Packet-dropping rules to dictate which packets should be dropped first in the event of buffer saturation Boundary nodes PHB mechanisms Traffic conditioning functions metering, marking, shaping, dropping

DS Traffic Conditioner

DS Traffic Conditioner (cont) Classifier Separates submitted packets into different classes Based on the DS codepoint or on multiple fields within the packet header Meter Measures submitted traffic for conformance to a profile Determines whether a given packet stream class is within or exceeds the service level guaranteed for that class

DS Traffic Conditioner (cont) Marker Polices traffic by re-marking packets with a different codepoint as needed Shaper Polices traffic by delaying packets as necessary so that the packet stream in a given class does not exceed the traffic rate specified in the profile for that class Dropper Drops packets when the rate of packets of a given class exceeds that specified in the profile for that class

ISA (IntServ) vs. DS (DiffServ)