IPv4 and Routing based on Chapter 8 of CompTIA Network+ Exam Guide, Mike Meyers
Routing How does a data packet get from its source network, to the destination's network? Individual networks are connected through the Internet The Internet is a network of routers also called a "network of networks"
Looking at Routes Routes can be discovered by: traceroute, tracepath Linux/MacOS programs tracert Windows program open visual traceroute open-source, cross-platform GUI program Some routes look surprising: trace to "unam.mx" for example
Open Visual Traceroute Cross-platform program to display IP routes http://visualtraceroute.net/ Download: Linux/Ubuntu: https://downloads.sourceforge.net/project/openvisualtrace/1.6.5/ovtr_1.6.5-1_amd64.deb?r=http%3a%2f%2fvisualtraceroute.net%2f&ts=1509228298&use_mirror=superb-sea2 Windows: https://downloads.sourceforge.net/project/openvisualtrace/1.6.5/openvisualtraceroute1.6.5.exe?r=htt p%3a%2f%2fvisualtraceroute.net%2f&ts=1509228377&use_mirror=cfhcable Install on VM-LAN virtual network Linux, Mac, or Windows, your choice
Installing into the VM-LAN virtual network Install whois and openjdk: sudo apt install whois openjdk-8-jre-headless Download OpenVisualRoute: browse to https://montcs.bloomu.edu/networking/software/o penvisualtraceroute/ download the Linux/Ubuntu package Install OpenVisualRoute: dpkg --install ovtr* Run the installed program.
Open Visual Traceroute unam.mx Display: Map; list of routers; graph of latency times
Creating a Route for a Packet Each router in the path chooses the next router to send the packet to, based on its IP address No router knows the entire path This is distributed knowledge So how does each router decide what "next" router to forward the packet to?
Topics Home Routers and Backbone Routers Routing Tables Dynamic Routing Distance Vector Link State BGP Hybrid Network Address Translation Working with Routers
Routers Routers: Receive an incoming packet on a port Inspect its IP address Choose an outgoing port based on the network ID portion of the IP address Forward the packet to that port IP addresses are layer 3 values so routers are layer 3 devices
Home Routers Home routers are actually multi-function devices Ethernet switch layer-2 device 802.11 Access Point layer-2 device two-port router layer-3 device Routers operate on two (or more) different networks the local one and the "Internet connection" This diagram shows a Linksys wireless router, implementing the Internet link and the local network as two VLANs ("Virtual LAN") The Access Point would be part of vlan0
Backbone Routers High-capacity routers handle multiple throughputs Example: Cisco XR12410 "core router" 10 slots 10 Gbps per slot 200 Gbps total throughput Many kinds of ports available to plug into slots Ethernet, SONET, FDDI, etc. $61,000 for a refurbished unit plus port adapters Dimensions: 37.5 inches high, 19 inches wide, 24 inches deep, 275 pounds
Configuring a router Web interfaces - Router has a built-in webserver - Home routers in particular Dedicated ports on the router itself - Requires physical access to the router - Generally on commercial routers - Cisco, et al provide their own configuration software and interfaces Network connection via SSH - Secure Shell encrypted network connection between nodes - Allows more secure remote access to routers
The Routing Function Many data packets are addressed to destinations on other networks than the source Broadcasting an ARP who-has to the entire Internet is impractical Packets must be moved from the source s network to the destination s network Routers must know how to get from network to network a routing animation: montcs.bloomu.edu/networking/simulations/tomsho/router.swf http://montcs.bloomu.edu/networking/simulations/tomsho/router.swf
Router Hops This transmission takes three hops from source router to destination router. Another route might take more, or fewer.
Routing Tables Router queues incoming packets layer-2 headers are discarded Packet's destination IP address is compared to entries in the router's routing table Best-matching entry in routing table provides: Gateway: IP address for next hop (next router) Interface: which router port to forward packet to
Basic Elements of a Routing Table Destination Subnet Mask Gateway Interface Metric 148.137.59.0 255.255.255.0 148.137.59.1 eth0 2 192.168.122.0 255.255.255.192 * virbr0 1 127.0.0.0 255.0.0.0 * (none) 1 0.0.0.0 (default) 0.0.0.0 148.137.59.1 eth0 2 Destination a network ID all directly connected networks are included Subnet mask description of entry s size Gateway IP address of the next-hop router Interface the appropriate outgoing port Metric "cost" in hops to use this route
A VyOS routing table Some routes (outlined in red) are indirect, going via another router metric is number of hops (intermediate routers) from this router to destination Default route (outlined in green) is used if no other entry matches This router has two default routes tied resolved by port number?
Linux Configured As A Router The "eth1" IP address is 172.16.0.1 Any 172.16.0.0/19 traffic goes through NIC "eth1" Any 192.168.122.0/24 traffic goes through "eth0" All other traffic goes through "eth0" to another router, at 192.168.122.1
A Windows client's routing table The route print command (or netstat r) displays and controls the host's routing table Default route is written as "0.0.0.0"
Routing Table Can t contain all possible IP addresses this would be nearly 4 billion entries! Destination Address Range Link Interface 11001000 00010111 00010000 00000000 through 0 11001000 00010111 00010111 11111111 11001000 00010111 00011000 00000000 through 1 11001000 00010111 00011000 11111111 11001000 00010111 00011001 00000000 through 2 11001000 00010111 00011111 11111111 4 billion possible entries otherwise 3
Longest prefix matching longest prefix matching when looking for forwarding table entry for given destination address, use longest address prefix that matches destination address. (Network ID) Binary Prefix Outbound Interface 0.0.0.0 / 0 3 200.23.16.0 / 21 11001000 00010111 00010 0 200.23.24.0 / 21 11001000 00010111 00011 2 200.23.24.0 / 24 11001000 00010111 00011000 1 Examples: which interface? DestAddr: 11001000 00010111 00010110 10100001 DestAddr: 11001000 00010111 00011000 10101010
Routing Algorithms
Topics Home Routers and Backbone Routers Routing Tables Dynamic Routing - Distance Vector - Link State - BGP - Hybrid Network Address Translation Working with Routers
Static and Dynamic Routing Static routing routing table entries are set up by hand - suitable for an internal router, direct connections Dynamic routing routing table entries are determined and maintained automatically, as connections change - Routing protocols use various algorithms to calculate routes
Distance Vector Algorithms Based on the Bellman-Ford algorithm Uses information about each router's neighboring routers Distributed algorithm Each router calculates what neighbor-router to forward a packet to Routing changes gradually propagate from router to router Sometimes called "Routing by rumor"
Bellman-Ford Distributed Algorithm Each router starts out knowing who it's connected to At each step, every router sends all it knows to its immediate neighbors So the immediate neighbors learn who the router knows about Eventually, all router connections are shared to all routers But each router only knows which immediate neighbor provides access to the other routers " I know a guy who knows a guy " Nobody has complete path information
RIP Routing Information Protocol Basic implementation of Bellman-Ford algorithm RIPv1 the original Internet/ARPAnet routing protocol Maximum hop count of 15 limited usable network size No security, no support for CIDR Updates every 30 seconds leads to traffic spikes RIPv2 adopted in 1994 CIDR support, authentication added Randomized update intervals
Link State Algorithms Link State protocols depend on each router knowing the entire network's topology - Aware of all other routers, all connections, and the cost of each connection Routers multicast link-state packets containing only their own (direct) connections and costs - Multicast to all other routers in an Autonomous System (AS network) Routers use a link-state routing algorithm to calculate least-cost path to any subnet - Dijkstra's algorithm is commonly used
Dijkstra s Algorithm 1 Initialization: 2 N' = {u} 3 for all nodes v 4 if v adjacent to u 5 then D(v) = c(u,v) 6 else D(v) = 7 8 Loop 9 find w not in N' such that D(w) is a minimum 10 add w to N' 11 update D(v) for all v adjacent to w and not in N' : 12 D(v) = min( D(v), D(w) + c(w,v) ) 13 /* new cost to v is either old cost to v or known 14 shortest path cost to w plus cost from w to v */ 15 until all nodes in N'
OSPF Open Shortest Path First Defined in RFC 2328 "Open" refers to open, public specification Links between routers have associated costs Link costs determined by the Network Administrator Cisco's formula: 10 8 / bandwidth-in-bps Costs: 10BaseT link: 10.0 100baseT link: 1.0 What will a 10GigE link cost? "Cost" is limited to integer values, so the formula fails for links faster than 100Mbps. A larger value than 10 8 needs to be used on router networks with higher-speed links.
an Example OSPF network "Traditionally, an elaborate OSPF network consists of a backbone area (area 0) and a number of areas connected to this backbone through an area border router (ABR)." -Cisco webpage
OSPF operation - 1 Each OSPF router broadcasts "Hello packets at first bootup - Known as "flooding" - Packets contain that router's connections and costs - Hello packets are one kind of Link State Advertisement (LSA) Routers accept Hello packets from other routers with the same Area ID - They shouldn't receive any others Routers forward received Hello packets to all other (connected) routers in the same Area
OSPF operation - 2 "Election process" identifies one router as Designated Router and another as Backup Designated Router - Network Admin can instead select DR and BDR DR and BDR then assemble, distribute complete network maps to other routers Each router computes its paths to subnets using Dijkstra's algorithm If a router changes one of its links it sends an LSA to the DR and BDR - DR, BDR forward new network map to other routers
OSPF Packet Types (LSAs) Hello Multicast (to 224.0.0.5) to establish communication with directly connected neighbors Database Descriptor (DBD) Lists router IDs from which the router has an LSA and its current sequence number Link State Request (LSR) Request for an LSA Link State Update (LSU) Reply to an LSR with the requested information Link State Acknowledgment (LSAck) Used to confirm receipt of link-state information
Comparing the Algorithms Distance Vector Each router announce all connections that it knows about, but only to its neighbors Distributed algorithm nobody computes an entire route Lots of information sharing, uses up network bandwidth Less computational work per router Link State Each router announces only its immediate neighbors, but all routers get the information Each router computes entire path to other routers More computation, but less information must be exchanged
Other Protocols
IS-IS Intermediate System to Intermediate System (pronounced "Eye-sys") Comparable to OSPF Uses a "Link State PDU" in place of OSPF's "LSA" Designed for non-ip networks Not based on IP packets - Links can still forward IP packets, however Supports IPv6 - Only newest revision of OSPF supports it Far less common than OSPF unfortunate
EIGRP the Hybrid Enhanced Interior Gateway Routing Protocol Combines characteristics of Distance Vector, Link State - Hence, hybrid protocol EIGRP is a Cisco proprietary protocol - Widespread, because Cisco routers are the Microsoft Windows of the router market
BGP Border Gateway Protocol A form of Distance-Vector algorithm Supports a hierarchical structure for the Internet Routes between Autonomous Systems instead of individual routers BGP-4 link
BGP and Autonomous Systems
Evolution of Autonomous Systems 1982 RFC 827 predicts "autonomous systems" "In the future, the internet is expected to evolve into a set of separate domains or "autonomous systems", each of which consists of a set of one or more relatively homogeneous gateways. The protocols, and in particular the routing algorithm which these gateways use among themselves, will be a private matter, and need never be implemented in gateways outside the particular domain or system." referred to in RFC 1267 1987: UUNET founded as first ISP operates as an AS
Autonomous Systems and RIRs By the 1990's the Internet had become too large for any protocol to work effectively across all routers 1992: IETF recommends reorganizing Internet into geographical regions 1995: RFC 1771 establishes BGP-4 for connecting AS's 1996: RFC 2050 recognizes five RIRs RIRs have authority to assign unique Autonomous System Numbers (ASNs) to AS organizations
BGP and AS's Each Autonomous System uses an Interior Gateway Protocol (IGP) to route between networks RIPv2, OSPF, EIGRP are common IGPs Autonomous Systems communicate with each other via an Exterior Gateway Protocol (EGP) Internet uses BGP-4 as the only EGP BGP can also be used as an IGP, if a particular Autonomous System chooses to
BGP, AS's, and IGPs BGP-4 connects these Autonomous Systems to each other 60000, 60001, 60002, 60003, 60004, 60005 Each Autonomous System uses its preferred Interior Gateway Protocols
RIRs Assign AS Numbers Geographically
AS Numbers IANA identifies AS's using Autonomous System Numbers (ASNs) - similar to IP addresses - specified in RFC-1930 as 16-bit values - written in decimal; e.g., AS3639 AS numbers 64512 65534 are private ASNs - AS numbers 0, 56320-6411 are reserved 2008: RFC-4893 introduced 32-bit AS numbers - Written in "dotted" notation - 16-bit numbers are a subset» viz., private ASN 64512 is equivalent to 0.64512
SSHENET - AS 22192 operated by PASSHE Contains 82 IPv4 prefixes Includes Bloomsburg, Lock Haven, Millersville, West Chester, etc. from: http://asrank.caida.org/?mode0=asinfo&mode1=asgraph&as=22192
some AS operators
Autonomous Systems - 2010 This diagram attempts to show regions according to their AS s US, UK, Russia have the most Distance from center indicates degree of locality Level 3, Cogent, Telianet are international 2010: ~24,000 AS s, ~60,000 interconnections source: www.ub.edu/web/ub/en/menu_eines/notici es/2010/09/10.html
Autonomous Systems - 2014
Summary Static routing - Network Admin configures every router by hand Dynamic routing - Router systems identify preferred routes automatically Routing algorithms for dynamic routing: - Distance-Vector» RIPv1, RIPv2» BGP primarily for AS-to-AS use - Link-State» OSPF, IS-IS - Hybrid - EIGRP