Chapter 7 - CCNA 2
Interior >> Gateway >> Protocols | Exterior >> Gateway >> Protocols
Distance Vector Contd
Cisco’s curriculum focuses on EIGRP, EIGRP IPv6, and both OSPFv2 & OSPFv3.
OSPF has both “single area” and “multi area”, we will focus on single area this semester (and chapter). We need to remember which one is, “What type?”
Distance Vector: Figures out how many hops a path is, takes the shorter length.
OSPF: Open Shortest Path First. OSPF is a Link State protocol because it takes into account how good the links are before making its decision.
EIGRP: Enhanced Interior Gateway Routing Protocol.
Purpose of Dynamic Routing Protocols
Why do we use dynamic routing protocols?
Here’s four examples why we use dynamic routing protocols:
- It will react to changing topologies.
- Choose best path for traffic.
- Maintain up-to-date routing tables.
- Discovers remote networks.
Dynamic versus Static
Dynamic needs setup (Easier than static).
Useful for default routes.
Dynamic uses more resources.
Useful for “STUB” networks.
Discovers networks automatically.
Not useful for larger networks.
Adapts to network changes.
Uses Less Resources (Less Overhead)
Auto-Updates the routing table.
Used for large networks.
STUB Network: Stub networks basically mean there’s only one way in, and one way out.
Unformatted Table Version of Protocols
PIPv2: IGP Distance Vector Classess
EIGRP: IGP Distance Vector Classless
OSPF: IGP Link State Classless
OSPF: IGP Link State Classless
IS-IS: IGP Link State Classless
BGP: EGP Path Vector Classless
Interior or Exterior Protocol
Type of Protocol
Classful / Classless
IGP: We want our speed of convergence (how fast it converges) and scalibility.
Autonomous System: Collection of routers under the same administration (common). A.S. - Routing Domain
IGP, or Interior Gateway Protocol: Used within an AS (Autonomous System). IGP has the capability to do Intra-Autonomous System.
EGP, or Exterior Gateway Protocol: Used between autonomous systems.
Used in scenarios like: If I have three routers that are AS 10, and three that are AS 20, so forth…
EGP is seldom used (except for Cisco tests, hehe), most of the time if they’re referring to EGP it normally means BGP (Border Gateway Protocol).
Distance Vector Protocol:
So, let's break down this definition.
- How far, hop count, bandwidth delay + cost.
- DIrection to a destination.
- Next Hop IP
- Exit Interface
DVP only knows the next-hop, not the destination.
Passive Interface Command
- Used on an interface without routers.
- Prevent routing updates going in direction.
- Smaller Networks
- When you want to use less bandwidth/less resources.
- Stub Networks
- Default Routes
- Auto Update Topology for Changes (Maintain routing table)
- Discovers Networks
Classless - Classful Routing
- No Subnet Mask Sent
- Only uses default subnet mask.
- Sends Subnet Mask
Which address will the IP 10.1.1.6 come out of?
10.1.1.6 10.1.0.0/30 via 10.1.3.4
10.1.1.0/24 via 10.1.4.1
10.1.3.0/28 via 10.4.1.1
If ‘10.1.0.0’ and the SM is /30, how many hosts will you have (bits)? 2
This means we can only have four addresses, period. It will run from 10.1.0.0 to 10.1.0.3.
You should be able to recognize from a /24 network it will match the first three octets, so “10.1.1” from the “10.1.1.6” address matches with the “10.1.1.0/24” network-- it will go out that interface.
What does this command do? “network 192.168.1.0”
Answer: This command will, when the router this command was entered on updates its routing table, it will broadcast something like, “Hey, I know how to get to 192.168.1.0! I have a route to it!”, making it available, otherwise known as “advertising” the address. Additionally, routing updates out all interfaces in that network.
What is the exterior gateway protocol?
BGP, see the table above (far above) if needed.
What is meant by “Convergence Time”?
Convergence time means the time it takes for all routers on the network to reach a consistent state, meaning they all agree what the routes are. Basically, it’s the amount of time it means for all the devices to “sync” and all have the same understanding of the network.
If in the routing table, an entry like as shown below…
D 172.16.0.64/26 (90/2170112) via 192.168.1.6 00:05:56 S0/0/1
What does this mean? Explain each part of this line.
- “D” is Dynamic Routing Protocol, learned from EIGRP.
- “172.16.0.64/26” is the destination address.
- “(90/2170112)” - The 90 means “Adminstrative Distance” or ‘AD’, and the 2170112 is the cost/metric. Note that if the AD (90) is 1 it means it’s a static route.
- “192.168.1.6” is the next-hop address.
- “00:05:56” is how long the device learned this route.
- “S0/0/1” is the exit interface, it would be the same if it was an IP address, but would be referred to as an “Exit Address”, or other terms.
Link State Protocols
Defined by SPF (Shortest Path First), built around a particular algorithm, which is “DIJKSTRA” (Dijkstra’s Algorithm), which will be expanded on in other chapters. Some Link State protocols are OSPF and IS-IS, and the configuration for Link State Protocols are relatively simple and the same as RIP, with minor command changes.
Note that Link State Protocols do not automatically send route updates, likewise, link state protocols send updates only when there are any modifications to the topology (topology changes), or less thought of, during initial startup.
In order for LSPs to do an update, two things must occur. First, Link State Protocols have to establish adjacencies, which means it basically has to ‘discover’ and link with it’s neighbor routes. Second, it has to establish the cost of its’ routes, meaning it has to figure out the next-hop cost from S0/0/0 to the next router's port.
Finally, Routing protocols don’t care about PCs or switches, only their router friends.
Which route would a packet from PC-A to PC-B go?
R1 > R3 > R4 > R5 = 12
Entry contains next-hop IP or exit interface.
Level 1 Route
A level 1 route means the route has a subnet mask equal or less than the classful subnet mask (Class C /24 or less).
Level 1 Parent Route
A level 1 route that has been subnetted. In the routing table you can find Lvl 1 Parent Routes if it says, “Variably Subnetted”, followed by or following a list of a subnet.
Level 2 Child Route
A level 2 child route is a route that is a subnet of a classful address. An example would be to take “172.16.0.0/16” (formerly the parent route) and subnet it to get something like (arbitrary, not valid) “172.16.3.0/24”, making this the parent route, and no longer a child.
The differences between an IPv6 and IPv6 table?
Since IPv6 is classless, it makes the addresses Ultimate, but for some reason, Cisco says “Level 1 Ultimate” routes.
If a router ever encounters a list of each type (Ultimate, Level 1… etc), which would it send out first?
The router would send out the ultimate route.
When we used RIP, what version did we use?
We used version two. This may not be useful to you as this is more of a specific, class-oriented note.
If I wanted to propagate a static default route (RIPng), what would I use?
The command would be exactly “default-information originate”, simply put.
This table is shown above in our notes, we refreshed our understanding of it so we did it again.
Protocols under which category, DV or LS:
Distance Vector versus Link State
RIPv2 OSPF v2/v3
Static Routing versus Dynamic Routing
Used for default routes. Auto-Discovery Network
Used for stub networks. Uses more resources
Not good for large networks. Auto-Adapts to Changes
Less resources. Auto-Updates Routing
Easier to Set Up
Pros & Cons of Link State
Hey, new table! The others aren’t put into one because they’ve been covered already, see above.
Bandwidth Intensive/High Consumption
Internally Builds a Topology Map