ITEC4610 Network Switching and Routing

ITEC4610Network Switching and Routing ดร. ประวิทย์ ชุมชู หัวหน้าสาขาวิชาวิศวกรรมสารสนเทศและการสื่อสาร(ICE) MUT Email: prawit@mut.ac.th ห้องทำงาน: F402 เบอร์โทรศัพท์ที่ทำงาน: (02)9883655 ต่อ 220 เบอร์โทรศัพท์เคลื่อนที่: 065343850

Class VIEIGRP(Enhanced Internal Gateway Routing Protocol) ดร. ประวิทย์ ชุมชู หัวหน้าสาขาวิชาวิศวกรรมสารสนเทศและการสื่อสาร(ICE) MUT Email: prawit@mut.ac.th ห้องทำงาน: F402 เบอร์โทรศัพท์ที่ทำงาน: (02)9883655 ต่อ 220 เบอร์โทรศัพท์เคลื่อนที่: 065343850

Outlines • กล่าวนำการทำงานของ EIGRP • การทำงาน EIGRP (Enhanced Internal Gateway Routing Protocol) • Neighbor discovery and Recovery • หลักการทำงานของ DUAL • Reliable Transport Protocol (RTP) • PDM (Protocol-dependent Module) • ประเภทของแพ็คเก็ตที่ใช้ในการสื่อสารระหว่างเร้าเตอร์ของ EIGRP • ตัวอย่างการสร้าง routing table ของ EIGRP • Summary

Routing Algorithms • Distance vector routing ถูกใช้ใน RIPv1 RIPv2 IGRP • Link-state Routing ถูกใช้ใน OSPF • Advanced distance-vector ถูกใช้ใน EIGRP • Dual (Diffusing Update Algorithm)

Distance vector routing • Initialization • เริ่มต้นสร้าง routing table • Sharing • การแลกเปลี่ยน routing table • Updating • การแก้ไข routing table • คำนวณเส้นทางโดยใช้ • Bellman-ford’s algorithm

Link-State routing • เริ่มต้นตรวจสอบสถานะของลิงค์ • แต่ละโหนดเก็บ link states ของตัวเอง • กระจาย link states ให้โหนดอื่นภายในพื่นที่ (flooding) • คำนวน shortest path ของจากโหนดตัวเองไปยังโหนดอื่น ๆ โดยใช้ • Dijktsta ‘a algorithm

ข้อดี ใช้หน่วยความจำน้อย การคำนวณไม่ซับซ้อน ข้อเสีย Slow convergence สามารถเกิด routing loop ข้อดี Fast convergence ข้อเสีย ใช้หน่วยความจำมาก การคำนวณซับซ้อนกว่า เปรียบเทียบ Distance-vector และ Link state

ตัวอย่างการทำงานของ RIP Node 2’s routing Table

ถ้า link 1-5 มีปัญหา • Node 2 ไม่สามารถส่งข้อมูลไปยัง Network A • รอจนเกิด timeout (90 second) • ใช้เวลาประมาณ 90-120 วินาทีในการที่จะได้เส้นทางใหม่ไปยัง ไปยัง network A โดยผ่านเร้าเตอร์ 3

EIGRP • Improved version of IGRP • Backwards compatible with IGRP • Improved convergence • Sends updates like a link state routing protocol • Supports VLSM/CIDR • Supports many layer 3 routed protocols (not just IP) • Routing protocol designed by Cisco • Combines best features of link-state and distance vector routing protocols • Compatible with IGRP • Two major versions • Version 0 • Version 1

EIGRP Protocol • Using DUAL • Neighbor Discovery and mechanisms • Reliable transportmechanism used to exchange update messages among routers that guarantee ordered delivery • Protocol dependent modules that enable its operation in a multiple-protocol environments such as IPX, IP, Apple talk

Five Types of EIGRP Packets • Hello packets (H) • Link Discovery • Update packets (U) • Update when a link change • ACK packets (A) • ACK for Update message • Query packets (Q) • Query Status of networks • Reply packets (R) • Reply to Query Messages

Neighbor Discovery and mechanisms • Link (neighbor) discovery and dead detection is used in determining when links appear and disappear • Small Hello messages are sent periodically • The hold time used to set a timer for duration of link up state after receiving hell message • Factors used in the metric computation • A link is discovery when the first hello packets is received (link up state) • A request is made of DUAL to send a full update to the link • A link down state occurs when • Hold down timer expires • Interface going down • A maximum retransmission threshold exceeded

Hello interval • 5-second hello: • Broadcast media, such as Ethernet, Token Ring and FDDI • Point-to-point links, such as PPP or HDLC leased circuits, Frame Relay point-to-point subinterfaces, and ATM • High bandwidth (greater than T1) multipoint circuit such as ISDN PRI and Frame Relay • 60-second hello: • Multipoint circuits T1 bandwidth or slower, such as Frame Relay multipoint interfaces, ATM multipoint interfaces • Switched virtual circuits and ISDN BRIs

Example of Hello packets

Neighbor Table • Neighbor table contains information about router’s neighbors including: • Neighbor address and interface • Hold time and Uptime • Smooth round trip timer (SRTT) • Retransmission timeout (RTO) • Handle (H) • Queue count • Sequence number

ตัวอย่าง The hold time=15 or 180 sec Hold = 10-15 sec, Hello interval =5 sec Hold = 120-180 sec, Hello interval =60 sec

หลักการทำงานของ DUAL(Diffusing Update Algorithm) • Topology Table • ต่างจาก LS • ไม่มีใน DV • Neighbor Table • ไม่มีใน LS & DV • Routing Table เหมือนกับ LS & DV DUAL quires its neighbors who, in turn, may query their neighbors and so forth….

Dual • Advance Distance Vector • Compute shortest path distributedly • No Routing Loop • No Counting-to-Infinity behavior • Performance better than DV • Performance similar to the performance of LS

Route States (two states) • Active - recomputation is being performed • Passive - no recomputation going on • If feasible successors are always available, a destination never goes into the active state. • Recomputation occurs when no feasible successor route exists • If a neighbor who is the only feasible successor to a destination goes down, all of the neighbor's routes enter the active state and trigger route recomputation. • Recomputation Process • Send a query packet to all neighboring routers • Neighbor sends • a reply that it has a feasible successor, or • a query packet to indicate it is partcipating in the recomputation • Routes in the active state cannot have their routing table information changed • Once all neighbors have replied the topology table entry for the destination returns to the passive state and the router may then select a feasible successor.

Topology table DN=Destination Network C=Cost RD=Report Distance RD=Feasible Distance

Report Distance (RD) • The cost to reach the destination N form router A • For example • A reports B: the cost to reach the destination N2 form router A is 12 (10+2)

Feasible Distance (FD) and successor • The lowest cost to reach a destinationis FD • The next hop router in the lowest cost path to the destination is referred to as the successor • For example • To reach N4, there are 2 paths: via C and A. The lowest cost is 12 via C, therefore FD =12, successor is router C

Feasible Successors (FS) • Feasible successor is next best route to destination • EIGRP may keep more than one feasible successor in its topology table • Next hop router must have reported distance (RD) to destination less than feasible distance of route of current successor • Helps prevent routing loops • For example (router B) • FS of N2=NULL, FS of N3=NULL, FS of N4=A • FS of N5=NULL

Building the Topology Table with Update Packets • Topology table consists of all the routes each neighbor advertises • Includes metrics advertised by neighbors for routes • Includes metric the router itself uses to forward packets to those destinations • Adds metric to get to neighbor to metric advertised by neighbor to destinations

Building and Maintaining Routing Tables • Building routing tables for first time • When router becomes part of EIGRP network, it sends out hello packets on all interfaces • Neighbor replies with update packets containing Init bit to indicate a new neighbor relationship. • New router acknowledges each update packet and uses information in packets to builds its topology table • New router then sends update packets to all neighbors • Each neighbor replies with an ACK • Seethe Table in the next slide

Building a Routing Table for the First Time • The new router sends packets hello packets out all of interfaces • A neighbor replies with a series of update packets • The new router sends an ACK packet for each update packet received • The new router builds its topology table with the information contained in the update packets • The new router sends update packets to all of its neighbors • Each neighbor replied with an ACK packet for each update packet it receives

Examples of Building a Routing Table for the First Time

Examples of Building a Routing Table for the First Time (cont.)

Failure of the Primary Route • DUAL algorithm looks at each feasible successor in topology database • Chooses one with lowest metric; does not have to recalculate it • If no feasible successor exists, router queries neighbors in query range with split horizon rule to find new route • New route goes from passive to active state and must be recalculated • If no response to query packet within time limit, router enters stuck-in-active (SIA) state

Topology Change on an EIGRP Network • When router joins network, it builds routing table, using information from neighbors. • If more than one possible path exists to a network, router chooses path with best feasible distances • If serial link goes down, router must find a new route to destination network

Convergence in DUAL—local computation

Convergence in DUAL—Diffusing computation

Transport Mechanism • Reliably • A mix of multicasts and unicasts • Multicast for first transmission, others using unicast • Sequence number for Acknowledging • A window size of one • Update message (multicast), query message (multicast), reply message (unicast) • Estimation of smooth round trip time (SRTT) • The retransmission timeout (RTO) is the time that the router will wait for an acknowledgement before retransmitting the packet

Transport Mechanism (cont.) • Unreliably • Acknowledgement packets • Hello packets • For IP • Protocol field is 88 • IP multicast address if 224.0.0.10

Examplefor Retransmission RTO?

Protocol Dependent Modules (PDM) • Response for initialization, building and decoding packets • Interfacing DUAL to the routing table • Proving protocol-dependent support routines for DUAL

EIGRP Metric • Five variables used to calculate metric • Bandwidth • Delay • Reliability • Load • Maximum transmission units (MTU) • Uses constants, called K-values, to calculate final metric • Final metric value multiplied by 256 results in a 32-bit metric value

Default K-values bandwidth (kbps) Delay (tens of microsecond)

ตัวอย่างการคำนวณ Metric B= bandwidth (kbps) d= Delay (tens of microsecond)

ตัวอย่างการคำนวณ metric • Metric=[K1*bandwidth+(K2*bandwidth)/(256-load)+K3*delay)]*[K5/(Reliability+K4)] • K1=1, K2=0, K3=1, K4=0, K5=0 • Metric =[bandwidth + delay] • No floating point, Round down • Router 1 to Network A • Via router 4 • (10,000,000/56+2200)*256=(180771+2200)*256=46277376 • Via router 3 • (10,000,000/128+1200)*256=(78125+1200)*256=79325*256=20307200 • Router 1 to Network A: Via router 3

Five Types of EIGRP Packets • Hello packet • Hello packets assist in the discovery of EIGRP neighbors. The packets are multicast to 224.0.0.10. • Update packets • Update packets contain the routing information of destinations. Update packets are unicast to newly discovered neighbors; otherwise, update packets are multicast to 224.0.0.10 when a link metric changes. Update packets are acknowledged to ensure reliable transmission. • ACK packets • An acknowledgment packet acknowledges the reception of an update packet. An acknowledgment packet is a hello packet with no data. Acknowledgment packets are sent to the unicast address of the sender of the update packet. • Query packets • Query packets are sent to find feasible successors to a destination. Query packets are always multicast. • Reply packets • Reply packets are sent to respond to query packets. • Reply packets provide a feasible successor to the sender of the query. • Reply packets are unicast to the sender of the query packet.

EIGRP packets • The destination IP address in EIGRP depends on the packet type--some packets are sent as multicast (with an address of 224.0.0.10) and others are sent as unicast • The source IP address is the IP address of the interface from which the packet is issued. • Following the IP header is an EIGRP header.

ITEC4610 Network Switching and Routing