Routing Protocols

Comparing VRRP and HSRP

* VRRP is an IEEE standard (RFC 2338) for router redundancy; HSRP is a Cisco proprietary protocol. * The virtual router that represents a group of routers is known as a VRRP group. * The active router is referred to as the master virtual router. * The master virtual router may have the same UP address as the virtual router group, * Multiple routers can functions as backup routers * VRRP is supported on Ethernet, Fast Ethernet, and Gigabit Ethernet interfaces as well as on Multiprotocol Label Switching (MPLS), virtual private networks (VPNs), and VLANs.

VRRP Redundancy Characteristics

* VRRP provides redundancy for the real IP address of a router or for a virtual IP address shared among the VRRP group members. * If a real IP address is used, the router with that address becomes the master. * If a virtual IP address is used, the master is the router with the highest priority. * A VRRP group has one master router and 1 or more backup routers. * The master routers uses VRRP messages to inform group members of its status. * VRRP allows load sharing across more than 1 virtual router.

HSRP >> HSRP Timers

*Hello Times* - The hello times is the defines interval during which each of the routers sen out Hello messages. Their default interval is 3 seconds, and they identify the state that each router is in. This is important because the particular state determines the specific role of each router and, as a result, the actions each will take within the group. This timer can be changed to milliseconds if you want. *Hold Timer* - Hold timer specifies the interval the standby router uses to determine whether the active router is offline or out of communication. By default, the hold timer is 10 seconds, roughly 3 times the default hello timer. If 1 timer is changed for some reason, it's recommended using 3x multiplier to adjust the other timers to. This is to avoid failover if there is short break in communication. *Active Timer* - Active timer monitors the state of the active router. The timer resets each time a router in the standby group receives a Hello packet from the active router. This timer expires based on the hold time value that's set in the corresponding field of the HSRP hello message. *Standby Timer* - Standby timer is used to monitor the state of the standby router. The timer resets anytime a router in the standby group receives a hello packet from the standby router and expires on the hold time value that's set in the respective hello packet.

IPv6 Routing Protocols >> OSPFv3

Adjacency (neighbor routers running OSPF) and next-hop attributes now use link-local addresses, and OSPFv3 still uses multicast traffic to send its updates and acknowledgements, with the addresses FF02::5 for OSPF routers and FF02::6 for OSPF designated routers, which provide topolocial updates (route information) to other routers. These new addresses are replacements for 224.0.0.5 and 224.0.0.6, respectively, which were uses in OSPFv2 (aka OSPF) *Shortest Path Bridging (SPB), specified in the IEE 802.1aq standard, is a computer networking technology intended to simplify the creating and configuration of networks and replace the older 802.1d/802.1w protocols, while enabling multipath routing*

Virtual Router Redundancy Protocol (VRRP)

Allows a group of routers of routers to form a single virtual router. A VRRP group has 1 master router and one or more backup router. Open standard.

Distance Vector Routing Protocols >> Border Gateway Protocol (BGP)

BGP is an EGP by default. It can be used within an AS which is why it's a hybrid protocol. It's known as a path vector protocol. BGP is essentially an alternative to using default routes for controlling path selection. *An autonomous system is a collection of networks under a common administrative domain. IGP operate within an autonomous system, and EGP connect different autonomous system together.* BGP would come in really handy if you wanted to multi-home a network for better redundancy, either to a multiple access point of a single ISP or to multiple ISPs. BGP doesn't broadcast its entire routing table like RIP; it updates a lot more like OSPF, which is a huge advantage. The routing table in BGP is called Routing Information Base (RIB). BGP also tells you about any/all networks reachable at the end of the path. BGP even gives you the history on how the networks at the end of the path were introduced into BGP in the 1st place, known as the origin code attribute.

OSPF and RIP comparison

Characteristics: Type of protocol OSPF: Link state RIPv2: Distance vector RIPv1: Distance vector Characteristics: Classless support OSPF: Yes RIPv2: Yes RIPv1: No Characteristics: VLSM support OSPF: Yes RIPv2: Yes RIPv1: No Characteristics: Auto-summerization OSPF: No RIPv2: Yes RIPv1: Yes Characteristics: Manual summarization OSPF: Yes RIPv2: No RIPv1: No Characteristics: Discontiguous support OSPF: Yes RIPv2: Yes RIPv1: No Characteristics: Route propagation OSPF: Multicast on change RIPv2: Periodic multicast RIPv1: Periodic broadcast Characteristics: Path metric OSPF: Bandwidth RIPv2: Hops RIPv1: Hops Characteristics: Hop-count limit OSPF: None RIPv2: 15 RIPv1: 15 Characteristics: Convergence OSPF: Fast RIPv2: Slow RIPv1: Slow Characteristics: Peer authentication OSPF: Yes RIPv2: Yes RIPv1: No Characteristics: Hierarchical network OSPF: Yes (Using areas) RIPv2: No (flat only) RIPv1: No (flat only) Characteristics: Updates OSPF: Event triggered RIPv2: Route table updates time intervals RIPv1: Route table updates Characteristics: Route computation OSPF: Dijkstra RIPv2: Bellman-Ford RIPv1: Bellman-Ford

Distance Vector Routing Protocols >> EIGRP

EIGRP is a classless, enhanced distance vector protocol that possesses a real edge over another older Cisco proprietary protocol, IGRP. EIGRP uses the concept of an autonomous system to describe the set of contiguous routers that run the same routing protocol and share routing information. EIGRP includes the subnet mask in its route updates. EIGRP is referred to as a hybrid routing protocol because it has characteristics of both distance and link state protocols. It sends distance vector updates containing information about networks, plus the cost of reaching them from the perspective of the advertising router. Its link state characteristics is that it synchronizes routing tables between neighbors at startup and then sends specific updates only when topology changes occur. EIGRP is suitable for very large networks. EIGRP features over RIP & RIPv2 * Support for IP and IPv6 (and some other useless routing protocols) via protocol-dependent modules. * Considered classless (same as RIPv2 and OSPF) * Support for VLSM/Classless Inter-Domain Routing (CIDR) * Support for summaries and discontiguous networks. *Efficient neighbor discovery. * Communication via Reliable Transport Protocol (RTP). * Best path selection via Diffusing Update Algorithm (DUAL). EIGRP uses *bandwidth* and *delay* of line as well as send *reliability*, *load*, and the *MTU* information between routers, but it only uses *bandwidth and delay by default*. Neighbor Table - Each router keeps state information about adjacent neighbors. When a newly discovered neighbor is learned on a router interface, the address and interface of that neighbor are recorded and the information is held in the neighbor table and stores in RAM. Sequence numbers are used to match acknowledgments with update packets. The last sequence number received from the neighbor is recorded so that out-of-order packets can be detected. Topology Table - is populated by the neighbor table, and the best path to each remote network is found by running Diffusing Update Algorithm (DUAL). The topology table contains all destinations advertised by neighboring routers, holding each destination address and a list of neighbors that have advertised the destination. For each neighbor, the advertised metric, which comes only from the neighbor's routing table, is recorded. If the neighbor is advertising this destination, it must be using the route to forward packets. Feasible Successor (Backup Routes) - is a path whose reported distance is less than the feasible (best) distance, and it is considered a backup route. EIGRP will keep up to six feasible successors in the topology table. Only the one with the best metric (the successor) is copied and placed in the routing table. Successor (Routes in a Routing Table) - is the best route to a remote network. A successor route is used by EIGRP to forward traffic to a destination and is stored in the routing table. It is backed up by a feasible successor route that is stored in the topology table - if one is available. *Route redistribution is the term used for translating from one routing protocol into another. An example would be where you have an old router running RIP and you have an EIGRP network. You can run route redistribution on one router to translate the RIP routes into EIGRP.*

High Availability

First hop redundancy protocols (FHRPs) works by making more than 1 physical router to appear as if they were only a single logical one. Clients are presented a virtual router in which they interact with virtual MAC and IP. Hot Standby Router protocol (HSRP) - Cisco proprietary protocol that provides a redundant gateway for hosts on a local subnet, but this isn't a load-balanced solution. HSRP allows you to configure 2 or more routers into a standby group that shares an UP address and MAC address and provides a default gateway. When IP and MAC addresses are independent from the routers' physical addresses, they can swap control of an address if the current forwarding and active router fails. But there is actually a way you can sort of achieve load balancing with HSRP - by using multiple VLANs and designating a specific router for one VLAN, then an alternate router as active for VLAN via trunking Virtual Router Redundancy Protocol (VRRP) - Almost identical to HSRP.

HSRP >> Virtual MAC Address

HSRP MAC address has only one variable piece in it. The 1st 24 bits still identify the vendor who manufactured the device ( the organizationally unique identifier, or OUI). The next 16 bits in the address tells us that the MAC address is a well-known HSRP MAC address. Finally, the last 8 buts of the address are the hex representation of the HSRP group number. Example 0000.0c07.ac0a * The 1st 24 bits (0000.0c) are the vendor ID of the address; in the case of HSRP being a Cisco protocol, the ID is assigned to Cisco. * The next 16 bits (07.ac) are the well-known HSRP ID. This part of the address was assigned by Cisco in the protocol, so it's always easy to recognize that this address is for use with HSRP. * The last 8 bits (0a) are the only variable bits and represent the HSRP group number that you assign. In this case, the group number is 10 and converted to hex when placed in the MAC address, when it becomes the 0a that you see.

Hot Standby Router Protocol (HSRP)

It defines a standby group, and each standby group that you define includes the following routers: * Active router * Standby router * Virtual router * Any other router that maybe attache to the subnet The problem with HSRP is that only 1 router is active and 2 or more routers just sit there in standby more and won't be used unless a failure occurs. Active and standby router communicate to each other via multicast Hello messages. If active router stops sending hello messages the standby router becomes the active one.

Link State Routing Protocols >> Intermediate System-to-Intermediate System (IS-IS)

L1 - Level 1 intermediate systems route within an area. When the destination is outside an area, they route toward a Level 2 system. L2 - Level 2 intermediate systems route between areas and toward other AS's. IS-IS uses Dijkstra's algorithms to discover shortest path. It uses Connectionless Network Service (CLNS) to provide connectionless delivery of data packets between routers, and it also doesn't require an area 0 like OSPF does. An advantage to having CLNS around is that is can easily send information about multiple routed protocols (IP and IPv6). OSPF must maintain a completely different routing database for IP and IPv6, respectively, for it to be able to send updates for both protocols. IS-IS is preferred by ISPs because of its ability to run IP and IPv6 without creating a separate database for each protocol as OSPF does.

EIGRP Tables

Neighbor Table-IP - Contains *Next Hop Router* and *Interface* >> Topology Table-IP - Contains *Destination 1, Destination 1* and *Successor* and *Feasible Successor* >> Routing Table-IP - Contains *Destination 1* and *Successor*

Link State Routing Protocols

OSPF and IS-IS are 2 examples. For a protocol to be a classless protocol, the subnet mask information must be carried with the routing update so routers can identify the best path. All neighbor routers know the cost of the network route that's being advertised. Link state routing maintains 2 other tables other than routing table. The 1st table is the neighbor table. It is maintained through hello packets by all routers to determine which other routers are available to exchange routing data with. All routers can share routing data are stored in the neighbor table. The 2nd table is the topology table, which is built and sustained through the use of link state advertisements or packets (LSAs or LSPs). In the topology table you'll find a listing for every destination network plus every neighbor (route) through which it can be reached. Essentially, it's a map of the entire internetwork. Once all of that raw data is shared and each one of the routers has the data in its topology table, the routing protocol runs the Shortest Path First (SFP) algorithm to compare it all and determine the best paths to each of the destination networks.

Link State Routing Protocols >> Open Shortest Path First (OSPF)

Open Shortest Path First (OSPF) is an open standard routing protocol. It works by using Dijkstra algorithm. 1st, a shortest-path tree is constructed, and then the routing table is populated with the resulting best paths. OSPF converges quickly (not as fast as EIGRP), and it supports multiple, equal-cost routes to the same destination. Like EIGRP, it supports both IP and IPv6 routed protocols, but OSPF must maintain a separate database and routing table for each IP and IPv6. OSPF provides the following features: * Consists of areas and autonomous systems * Minimizes routing update traffic * Allows scalability * Supports VLSM/CIDR * Has unlimited hop count * Allows multi-vendor deployment (open standard) * Uses a loopback (logical) interface to keep the network stable One of OSPF's most noteworthy features is that after a network change, such as when a link changes to up or down, OSPF converges with serious speed. Convergence refers to when all routers have been successfully updated with the change. OSPF is supposed to be designed in a hierarchical fashion, which means you can separate the larger internetwork into smaller internetworks called areas. The reason you want to create OSPF in a hierarchical design: * To decrease routing overhead * To speed up convergence * To confine network instability to single areas of the network OSPF must have an area 0, and all other areas should connect to this area. ROuters that connect other areas to the backbone area within an AS are called area border routers (ABRs). Still, at least one interface of the ABR must be in area 0. The router that connects multiple AS's is called an autonomous system border router (ASBR). Typically, in today's networks, BGP is used to connects between AS's not OSPF.

IPv6 Routing Protocols

RIPv1 & v2 >> RIPng EIGRP >> EIGRPv6 OSPF >> OSPFv3

Default Administrative Distances (AD)

Route source = Connected interface Default AD = 0 Route source = Static route Default AD = 1 Route source = External BGP Default AD = 20 Route source = Internal EIGRP Default AD = 90 Route source = IGRP Default AD = 100 Route source = OSPF Default AD = 110 Route source = ISIS Default AD = 115 Route source = RIP Default AD = 120 Route source = External EIGRP Default AD = 170 Route source = Internal BGP Default AD = 200 Route source = Unknown Default AD = 255 (this route will never be used)

Routing flow tree

Routing >> Static Routing, Dynamic routing Dynamic Routing >> IGP, EGP (Protocols: BGP) IGP >> Distance Vector (Protocols: RIPv1 & 2, IGRP), Link State (Protocols: OSPF, IS-IS) Distance Vector, Link State >> Hybrid (Protocols: EIGRP, BGP)

Distance Vector Routing Protocols

Routing Information Protocol (RIP) - Sends complete routing table out to all active interfaces every 30 seconds. Only uses hop count to determine best path. Has maximum allowable hop count of 15 by default, a hop count of 16 would be deemed unreachable. Slow to converge. Uses classful routing meaning all devices in the network must use the same subnet mask for each specific class. RIPv2 provides something called prefix routing and does send subnet mask info with the route updates allowing classless routing. RIPv1: Distance vector RIPv2: Distance vector RIPv1: Max hop count of 15 RIPv2: Max hop count of 15 RIPv1: Classful RIPv2: Classless RIPv1: Broadcast based RIPv2: Uses multicase 224.0.0.9 RIPv1: No support for VLSM RIPv2: Supports VLSM networks RIPv1: No authentication RIPv2: Allows for MD5 authentication RIPv1: No support for discontiguous networks RIPv2: Supports dscontiguous networks

IPv6 Routing Protocols >> RIPng

The primary features of RIPng are the same as they were with RIPv2. Still distance vector, max hop count 15, as well as using UDP port 521. Still uses mutlicast to send its updates but in IPv6, it uses FF02::9 vs RIPv2 address 224.0.0.9 Routers keep the next-hop addresses of their neighbor routers for every destination network in their routing table. The difference is that with RIPng, the router keeps track of this next-hop address using the link-local address, not a global address.

Classes Of Routing Protocols

There are 3 mentioned but there are more Distance Vector - Finds best path to a remote network distance. Each time a packet goes through a router, it equals a hop. The route with the fewest hops to the destination network will be chosen as the best path. The vector indicates the direction to the remote network. RIP, RIPv2 and Interior Gateway Routing Protocol (IGRP) are distance vector routing protocols. These protocols send the entire routing table to all directly connected neighbors. Link State - also known as shortest path 1st protocols. The routers each create 3 seperate tables. 1 of these tables keeps track of directly attached neighbors, 1 determines the topology of the internetwork, and 1 is used as the actual routing table. Link state routers know more about the internetwork than any distance vector routing protocol. OSPF and IS-IS are IP routing protocols that are completely link state. Link state protocols send updates containing the state of their own links to all other routers on the network. Hybrid - uses aspects of both distance vector and link state. EIGRP, BGP (when used as iBGP but commonly used as an EGP) .

Administrative Distances (AD)

Used to rate the trustworthiness of routing information received on once router from its neighboring router. An AD is an integer from 0 to 255, where 0 equals the most trusted route and 355 the least. A value of 255 essentially means, "No traffic is allowed to be passed via this route." If a router receives 2 updates listing the same remote network, the 1st thing the router checks is the AD. If one of the AD is lower than the other it will get placed in the routing table. If both AD are the same then routing protocol metrics like hop count or the amount of bandwidth on the lines will be used to find the best path to the remote network. AD with lowest metric will be placed in routing table. If both ADs have same AD and same metric then the routing protocol will load-balance to the remote network.

Distance Vector Routing Protocols >> VLSM and Discontiguous Networks

VLSM works with assigning addresses to group(s) which has most users and works up the subnet addresses to least amount of users. If you have a /24 you can break that down smaller subnets which adds back up to your /24 and this just helps with saving address space. VLSM works with routing protocols like RIPv2, EIGRP, OSPF. Does Not work with RIPv1 or IGRP A discontiguous network is one that has 2 or more subnetworks of a calssful network connected together by different classful networks. Works with OSPS by default because it does not auto-summarize like RIPv2 and EIGRP. Does NOT work with RIPv1. By default it won't work with RIPv2 or EIGRP * Route aggregation is essentially combining multiple subnets into one larger subnet, and it's also known as supernetting. You would implement this type of route summarization if you required more efficient routing tables in large networks.*

IPv6 Routing Protocols >> EIGRPv6

similar to EIGRP is terms of features and how it operates. EIGRPv6 multicast address is FF02::0 vs 224.0.0.10 is EIGRP.