ITEC4610 Network Switching and Routing ดร. ประวิทย์ ชุมชู หัวหน้าสาขาวิชาวิศวกรรมสารสนเทศและการสื่อสาร(ICE) MUT Email: prawit@mut.ac.th ห้องทำงาน: F402 เบอร์โทรศัพท์ที่ทำงาน: (02)9883655 ต่อ 220 เบอร์โทรศัพท์เคลื่อนที่: 065343850

Class VI EIGRP (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

Objectives การทำงานของ DUAL การทำงาน EIGRP Neighbor discovery and Recovery Reliable Transport Protocol (RTP) Dual-finite State machine PDM (Protocol-dependent Module) ประเภทของข้อมูลที่ใช้ในการสื่อสารระหว่างเร้าเตอร์

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

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

ตัวอย่างการทำงานของ RIP Node 2 ’s routing Table Dst Next-hop Cost A Node 1 2 ...

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

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

ตัวอย่างการทำงานของ DUAL Node 1 ’s Topology Table Network Via Feasible Distance Advertised distance Added to topology/routing table? A Node 1 2 1 yes /yes Node 2 3 yes /no … ..

ถ้า link 1-5 มีปัญหา Node 2 ไม่สามารถส่งข้อมูลไปยัง Network A

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

Advantages of EIGRP Rapid convergence Low routing update traffic Support for multiple protocols Support for VLSMs and classless routing Support for route summarization along arbitrary boundaries

EIGRP Features Hellos sent every 5 secs Neighbour table Topology table DUAL takes information in neighbour & topology table and calculates best routes (‘successors’) and adds them to the Routing Table ‘Feasible successors’ are alternative, backup routes

Hybrid Routing Protocol Features Hybrid of link-state and distance vector routing protocols Learns routes from connected interfaces or their neighbors Does not need to know entire network topology Does not require much memory or CPU to calculate routing tables Saves bandwidth by sending routing updates only to routers that need the information

EIGRP Strategies to Avoid Routing Loops Uses Diffusing Update Algorithm (DUAL) Routers store back-up routes by using topology table Topology table contains only routes advertised by neighboring routers Comparison of EIGRP with RIP and OSPF RIP is pure distance vector routing protocol OSPF is pure link-state routing protocol การพิสูจน์ว่าไม่มี Loop สามารถอ่านเพิ่มเติม J.J.Garcia-Luna-Aceves, “Loop-Free Routing Using Diffusing computations,” IEE/ACM networking, Vol. 1, No. 1, February 1993.

EIGRP Operation Uses hello packets to identify neighbors Uses reliable transport to exchange routing information Stores information about neighbors and their routes Uses this information to build routing tables

EIGRP Technologies Hellos multicast every 5 seconds to 224.0.0.10 Holdtime (route dead) - 3 x hello interval RTP used as a reliable transport protocol to remain protocol independent Sequence numbers used on replies/acknowledgements to hellos – unicast NOT multicast Multicast update packets sent when topology changes

Transmission of EIGRP Packets On IP network, EIGRP uses IP packets Identified as protocol 88 in the IP header Reliable Transport Protocol (RTP) has sequence number in each packet Requires explicit acknowledgement for each packet sent reliably RTP builds transmission list for each neighbor and retransmits up to 16 times or until hold time expires

Multicast Packets with EIGRP Multicast packet to all neighbors is more efficient than multiple hello packets requiring acknowledgement RTP flag in packet indicates no acknowledgement is necessary RTP flag also used in packets carrying routing updates

Five Types of EIGRP Packets Hello packets Update packets ACK packets Query packets Reply packets

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.

An EIGRP header The fields following the EIGRP header depend on the opcode field.

IP internal route updates -Type field of 0x0102 -The next hop identifies the router to send packets destined for destination -The prefix length field signifies the subnet mask

IP external route updates

Building and Maintaining Neighbor Relationships Hello packets discover and maintain relationships with neighboring routers Packets sent at hello interval Default is 5 seconds for fast interfaces and up to 60 seconds for slower links Default hold time is three times the hello interval but may be up to 180 seconds for slower links Hello interval and hold time may be configured independently

Exchanging Neighbor Information in Hello Packets To become neighbors, routers must share Common subnet Same Autonomous System number Same constants to calculate EIGRP’s metric

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

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 See the Table in the next slide

Building a Routing Table for the First Time

Building Routing Tables Uses DUAL algorithm to select primary and back-up routes for each destination Includes these routes in its topology table Supports internal, external, and summary routes Adds best route into routing table as successor route

ตัวอย่างการคำนวณด้วย 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

Maintaining Routing Tables with the DUAL Algorithm DUAL is a finite state machine Each state is loop-free routing table DUAL watches for topology changes Selecting best path with DUAL Algorithm Advertised distance (AD) or lowest cost is advertised to neighbors Feasible distance (DF) is total metric to destination Successor or lower cost loop-free path is added to routing table Current successor is primary route to any destination

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 pasive state and the router may then select a feasible successor.

Selecting Feasible Successors 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 advertised distance to destination less than feasible distance of route of current successor Helps prevent routing loops

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

Example Network

Router A’s Possible Topology Table Entries

Network with Serial Interface Down

Using EIGRP on Very Large Networks Use special care to minimize routing problems and convergence time EIGRP scalability is affected by variables Number of routers involved in network change Amount of routing information exchanged by EIGRP neighbors Number of hops information travels to reach all affected routers Number of redundant paths on network

Restrict and Eliminate Queries Lost reply packets result in serious convergence problems Heavy CPU or memory usage on router causes problems The larger the query scope in an Autonomous System, the more likely routers are to end up in SIA mode Size of query depends on number of neighbors and number of paths a query might take

Restricting Query Scope Segment a network into multiple Autonomous Systems May not solve problem Use route summarization Summary routes must be placed appropriately

Restricting Queries with Multiple EIGRP Autonomous Systems

Route Tagging Internal routes come from neighbors with the same (E)IGRP AS number or from directly attached interfaces over which IGRP or EIGRP runs. External routes come from other routing protocols or from static routes and are tagged with the following information: Router ID of the router that distributed the route AS number of the destination Configurable administrator tag ID of the external protocol Metric from the external protocol Bit flags for default routing

เปรียบเทียบ

Disadvantages of EIGRP Proprietary to CISCO Routers from other vendors cannot use or understand EIGRP

ตัวอย่าง ลองสร้าง Topology Table ของ router 1 ดู ลองสร้าง Routing Table ของ router 1 ดู

Node 1 ’s Topology Table A Node 1 2 1 yes /yes Node 2 3 yes /no … .. Network Via Feasible Distance Advertised distance Added to topology/routing table? A Node 1 2 1 yes /yes Node 2 3 yes /no … ..

ตัวอย่าง LS routing ลองสร้าง Topology Table ของ router 1 ดู ลองสร้าง Routing Table ของ router 1 ดู

ตัวอย่าง DV routing ลองสร้าง Topology Table ของ router 1 ดู ลองสร้าง Routing Table ของ router 1 ดู