It says we are receiving a packet with type 2 authentication while we use type 0. This means R1 is configured for no authentication while R2 is using MD5 authentication. In case you are wondering The message is self-explanatory, seems we have a mismatch in the area number.
Time to fix this! This time R1 and R2 are in area 1. R1 show ip ospf neighbor R2 show ip ospf neighbor What a surprise…no neighbors! OSPF has different area types and both routes have to agree on the area type stub, nssa, totally stub and totally nssa.
R1 show ip protocols include area Number of areas in this router is 1. R2 show ip protocols include area Number of areas in this router is 1. Most people have learned that OSPF always requires at least area 0 the backbone area. This is the default for Ethernet interfaces.
This is the reason they are stuck in the 2WAY state. You can see R1 has been elected for the DR because it has a priority of 1. Make sure one of the routers gets elected. We have 2 routers connected to each other running frame-relay.
This proves that broadcast capabilities for frame-relay have been enabled. The default network type is Non-Broadcast. This means OSPF expects us to configure the neighbors ourselves! Any other way to fix this? You should be able to fix these issues after reading this chapter! R1 show run section router ospf router ospf 1 log-adjacency-changes network R2 show ip route include This issue might sound a bit lame but using the wrong network statements is something that happens all the time.
Lesson learned: Make sure you configure the correct network address, wildcard bits and area. Same 2 routers but another issue. Here are the routing tables: R1 show ip route C R1 show ip protocols begin Networks Routing for Networks: R1 show access-lists Standard IP access list 1 10 deny 2. R1 config router ospf 1 R1 config-router no distribute-list 1 in This will disable it. Area 2 is not directly connected to area 0 so a virtual link has been created.
The virtual link is down. Note the IP addresses that we see here, those are the IP addresses that are configured on the FastEthernet interfaces of both routers. R1 show run incl virtual-link area 12 virtual-link R1 config router ospf 1 R1 config-router no area 12 virtual-link R1 show ip route ospf 2. R2 will redistribute network 2. R2 show ip route include 2. R2 show ip protocols Routing Protocol is "ospf 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 2.
This should include network 2. What could be a possible reason for this? R2 show ip protocols include areas Number of areas in this router is 1. Stub areas do not allow LSA type 5 external routes. We can either turn this area into a normal area or a NSSA.
R1 show ip route include 2. Either change the area to NSSA to stop redistributing. In the picture above we have R1 and R2 and the Here are the OSPF configurations: R1 show run section router ospf router ospf 1 log-adjacency-changes network Use the default-information originate always command.
R2 config ip route 0. R2 config no ip route 0. Here are the OSPF configurations: R1 show run section router ospf router ospf 1 log-adjacency-changes network 1. If you look closely at the output above you can already see something funky is going on. R1 show ip ospf database router R1 is telling me adv router is not-reachable.
This will prevent our routers from installing routes into the routing table! The network type is different…broadcast on R2 and point-to- point on R1. If you type in redistribute connected OSPF will only redistribute classful networks. R2 config router ospf 1 R2 config-router redistribute connected subnets I need to add the subnets keyword to make it redistribute subnets of major networks.
Redistribution can be complex and there are multiple solutions how you can solve redistribution issues. In the topology above we have 4 routers. The hop count is 1 for both paths. If you look at the picture you can see that it would be better to send it to R1. This router wants to send traffic for R4 show ip route ospf O E2 It has learned about network They only care about the path with the lowest metric. The same thing applies for prefix R2 show run section rip router rip version 2 redistribute ospf 1 metric 1 network R2 show run section ospf router ospf 1 log-adjacency-changes redistribute rip metric 1 subnets network In this scenario we can adapt OSPF so it will make a difference between the administrative distance of internal and external prefixes.
The administrative distance for external OSPF prefixes is now Does this make a difference? R3 show ip route R The routing tables of R2 and R3 are now looking good.
Because of these changes something changed on R4 however: R4 show ip route ospf O E2 The best path however would be through R2.
Network This happens because R2 and R3 both have network We can fix this by playing with the metric of OSPF. We can do the same thing for Whenever something matches access-list 1 it will set the metric to Access-list 1 matches network R4 only has a single entry now for network R4 show ip ospf database include This is good because if R3 fails we still have a backup path through R2. I want to make sure R4 uses R2 as the primary path to reach this network.
R4 is now using the most optimal path to reach network R1 show ip route rip R Looks like we are done here! Lesson learned: Use the administrative distance to prevent or allow the installation of prefixes in your routing table s and use the metric to select the best path.
Redistribution is not easy and there are multiple ways to solve issues. Make sure you are very familiar with routing protocols, administrative distance and path selection. Think about a solution first before implementing it. R2 is supposed to summarize network R1 show ip route ospf What went wrong here?
R2 show run section router ospf router ospf 1 log-adjacency-changes summary-address R1 show ip route ospf O IA You made it to the end of the OSPF chapter! We can use the show ip bgp summary command to check the IP addresses of the routers, these seem to match.
Our BGP neighbor adjacency is established…told you this one would be easy ; Lesson learned: Make sure your interfaces are up and running.
The next scenario is similar but slightly different. We are using the same routers and AS numbers but this time the BGP neighbor adjacency has to be established between the loopback interfaces. R1 show ip bgp summary BGP router identifier We are not using the directly connected links so we might have routing issues. Both routers only know about their directly connected networks.
R1 config ip route 2. R1 ping 2. R1 config-router neighbor 2. You can clearly see that R2 is using IP address What could possibly be wrong? What about L3? We could have issues with the transport layer. R1 telnet This should ring a bell, maybe something is blocking BGP? This one is similar to the EBGP situation earlier We could fix this with a static route or an IGP. Make sure these loopbacks are reachable and that the BGP updates are sourced from the loopback interface.
These are all the BGP neighbor adjacency related issues I wanted to show you. All routers will have working BGP neighbor adjacencies. R1 and R2 are in different autonomous systems. We are trying to advertise network 1. Here are the configurations: R1 show run section bgp no synchronization bgp log-neighbor-changes network 1. R2 show ip bgp summary BGP router identifier If we configure a network command for BGP it has to be an exact match. In this case I forgot to add the subnet mask… R1 config router bgp 1 R1 config-router network 1.
Lesson learned: Type in the exact correct subnet mask…BGP is picky! The network engineer from AS1 wants to advertise a summary to AS 2.
R1 show run section router bgp router bgp 1 no synchronization bgp log-neighbor-changes aggregate-address You can see the aggregate-address command on R1 for network If we want to advertise a summary we have to put something in the routing table of R1 first. Let me show you the different options: R1 config interface loopback 0 R1 config-if ip address R2 show ip route bgp By default it will still advertise the other prefixes.
Let me show you option 2 of advertising the summary: R1 config ip route R2 show ip route bgp B Create a static route and point it to the null0 interface to create a loopback interface that has a prefix that falls within the summary address range. You are working as a network engineer for AS 1 and one day you get a phone call from the network engineer at AS 2 asking you why you are advertising a summary for 1. You have no idea what the hell he is talking about so you decide to check your router.
R2 show ip route bgp B 1. R1 show ip bgp 1. R1 show ip route 1. This could mean only 1 thing…. R1 show ip protocols Routing Protocol is "bgp 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set IGP synchronization is disabled Automatic route summarization is enabled GNS3Vault.
R2 show ip route bgp 1. Lesson learned: If you see classful networks in your BGP table you might have auto-summary enabled. There could be a switch or another router in between the devices you are trying to troubleshooting that are causing issues. Using the appropriate show and debug commands will show you exactly what your router is doing and what it is advertising to other routers.
The people from AS 2 are complaining that they are not receiving anything from AS 1. Keep in mind that besides distribute-lists we can use also use route-maps for BGP filtering. R1 config router bgp 1 R1 config-router no neighbor Lesson learned: Make sure there are no route-maps blocking the advertisement of prefixes. BGP can be slow sometimes especially when you are waiting for results as you are doing labs. R1 is advertising network 1. Here are the configurations: R1 show run section router bgp router bgp 1 no synchronization bgp log-neighbor-changes network 1.
Technically there is no problem. In order to fix this we need to configure R1 and R3 to become neighbors. R1 config router bgp 1 R1 config-router neighbor Lesson learned: IBGP neighbor adjacencies have to be full mesh! Another solution would be by using a route-reflector or confederation. R3 is advertising network 3. Here are the configurations: R1 show run section router bgp router bgp 1 no synchronization bgp log-neighbor-changes neighbor R2 show ip route bgp 3. For some reason BGP is unable to install this entry in the routing table.
Take a close look at the next hop IP address Is this IP address reachable? R1 show ip route R2 config router bgp 1 R2 config-router neighbor The next hop IP address is now R1 show ip route bgp 3. Are we done now? R1 and R2 both have network 3. You can see in the routing table that it has no idea where to send IP packets meant for R3 show ip route bgp B R1 ping 3.
Lesson learned: Make sure the next hop IP address is reachable so routes can be installed in the routing table and that all required networks are reachable. These are all the BGP issues I wanted to show you so you made it to the end of this chapter. In this scenario we have 3 devices.
The device on the right side is supposed to be some webserver, something on the Internet that we are trying to reach on the Internet. Users from our LAN are complaining that they are unable to reach anything on the Internet. They have confirmed that their IP address and default gateway is OK. NAT telnet You can see that this is working so routing between the NAT router and the webserver plus connecting to the TCP port is no problem. The outside local and global IP addresses refer to the IP address on the inside.
You can see that the inside and outside interfaces have been swapped. Host ping The inside local IP address is our inside host. The outside local and GNS3Vault. Lesson learned: Make sure you have the correct inside and outside interfaces. Same topology, different problem! Once again users from the inside are complaining that they are unable to reach the webserver. There are no translations going on however.
The inside source has been defined by using access- list 1. Lesson learned: Make sure you use the correct access-list to match your inside hosts. Users from our LAN however are complaining that they are unable to reach the webserver. NAT show ip route include Open Our NAT router can reach the webserver so connectivity is not the problem. There is one important thing to keep in mind however. The source IP address is This makes sense because the However if we send a ping from the host device it is being translated because of NAT to an IP address in the The IP packet will look like this: Source: Destination: The ISP router receives the IP packet and will check its routing table if it knows where to send traffic for network The The webserver wants to respond and it will create a new IP packet with destination IP address The ISP router has to do a routing table lookup to see if it knows where network The ISP router has no idea where It tells us that it has no idea where to send the IP packet for So how do we solve this issue?
The ISP router requires network Next step is to advertise this network in BGP. Lesson learned: Make sure your routers know how to reach the translated networks.
The Client however is not receiving any IP addresses…what could be wrong? This is looking fine to me. Show ip sockets shows us on which ports the router is listening. Now we see the router is listening on port 67, this means the DHCP service is active.
Take a look at the scenario above. If you are a talent, you will receive that everything you want and even you can be the president of the country. When configuring, I have encountered a lot of problems. I will record it here for your reference. No valid license found.
Next Reboot license Level: lanbase. Inside is PAK. This must be taken care of when everyone is dismantling. In the event that the second worker was dismantled, the white paper tape was lost.
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