When you earned your CCNA, you thought you learned everything there is to know about RIP. Close, but not quite! There are some additional details you need to know to pass the BSCI exam and get one step closer to the CCNP exam, and one of those involves RIP update packet authentication.
You're familiar with some advantages of using RIPv2 over RIPv1, support for VLSM chief among them. But one advantage that you're not introduced to in your CCNA studies is the ability to configure routing update packet authentication.
You have two options, clear text and MD5. Clear text is just that - a clear text password that is visible by anyone who can pick a packet off the wire. If you're going to go to the trouble of configuring update authentication, you should use MD5. The MD stands for "Message Digest", and this is the algorithm that produces the hash value for the password that will be contained in the update packets.
Not only must the routers agree on the password, they must agree on the authentication method. If one router sends an MD5-hashed password to another router that is configured for clear-text authentication, the update will not be accepted. debug ip rip is a great command for troubleshooting authenticated updates.
R1, R2, and R3 are running RIP over a frame relay cloud. Here is how RIP authentication would be configured on these three routers.
R1#conf t
R1(config)#key chain RIP
< The key chain can have any name. >
R1(config-keychain)#key 1
< Key chains can have multiple keys. Number them carefully when using multiples. >
R1(config-keychain-key)#key-string CISCO
< This is the text string the key will use for authentication. >
R1(config)#int s0
R1(config-if)#ip rip authentication mode text
< The interface will use clear-text mode. >
R1(config-if)#ip rip authentication key-chain RIP
< The interface is using key chain RIP, configured earlier. >
R2#conf t
R2(config)#key chain RIP
R2(config-keychain)#key 1
R2(config-keychain-key)#key-string CISCO
R2(config)#int s0.123
R2(config-subif)#ip rip authentication mode text
R2(config-subif)#ip rip authentication key-chain RIP
R3#conf t
R3(config)#key chain RIP
R3(config-keychain)#key 1
R3(config-keychain-key)#key-string CISCO
R3(config)#int s0.31
R3(config-subif)#ip rip authentication mode text
R3(config-subif)#ip rip authentication key-chain RIP
To use MD5 authentication rather than clear-text, simply replace the word "text" in the ip rip authentication mode command with md5.
Here's what a successfully authentication RIPv2 packet looks like, courtesy of debug ip rip. Clear-text authentication is in effect and the password is "cisco".
3d04h: RIP: received packet with text authentication cisco
3d04h: RIP: received v2 update from 150.1.1.3 on Ethernet0
3d04h: 100.0.0.0/8 via 0.0.0.0 in 1 hops
3d04h: 150.1.2.0/24 via 0.0.0.0 in 1 hops
Here's what it looks like when the remote device is set for MD5 authentication and the local router is set for clear-text. You'll also see this message if the password itself is incorrect.
3d04h: RIP: ignored v2 packet from 150.1.1.3 (invalid authentication)
"Debug ip rip" may be a simple command as compared to the debugs for other protocols. but it's also a very powerful debug. Start using debugs as early as possible in your Cisco studies to learn how router commands really work!
Showing posts with label packet. Show all posts
Showing posts with label packet. Show all posts
Thursday, December 25, 2008
Cisco CCNP / BCSI Exam Tutorial: Configuring EIGRP Packet
Configuring RIPv2 and EIGRP authentication with key chains can be tricky at first, and the syntax isn't exactly easy to remember. But for BSCI and CCNP exam success, we've got to be able to perform this task.
In a previous tutorial, we saw how to configure RIPv2 packet authentication, with both clear-text and MD5 authentication schemes. EIGRP authentication is much the same, and has the text and MD5 authentication options as well. But EIGRP being EIGRP, the command just has to be a little more detailed!
As with RIPv2, the authentication mode must be agreed upon by the EIGRP neighbors. If one router's interface is configured for MD5 authentication and the remote router's interface is configured for text authentication, the adjacency will fail even if the two interfaces in question are configured to use the same password.
We'll now configure link authentication on the adjacency over an Ethernet segment. Below, you'll see how to configure a key chain called EIGRP on both routers, use key number 1, and use the key-string BSCI. Run show key chain on a router to see all key chains.
R2(config)#key chain EIGRP
R2(config-keychain)#key 1
R2(config-keychain-key)#key-string BSCI
R2#show key chain
Key-chain EIGRP:
key 1 -- text "BSCI"
accept lifetime (always valid) - (always valid) [valid now]
send lifetime (always valid) - (always valid) [valid now]
R3(config)#key chain EIGRP
R3(config-keychain)#key 1
R3(config-keychain-key)#key-string BSCI
R3#show key chain
Key-chain EIGRP:
key 1 -- text "BSCI"
accept lifetime (always valid) - (always valid) [valid now]
send lifetime (always valid) - (always valid) [valid now]
The EIGRP command to apply the key chain is a bit of a pain to remember, because the protocol and AS number is identified in the middle of the command, not the beginning. Also note that two commands are needed - one to name the key chain, another to define the authentication mode in use.
R2(config)#interface ethernet0
R2(config-if)#ip authentication key-chain eigrp 100 EIGRP
R2(config-if)#ip authentication mode eigrp 100 md5
5d07h: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.23.3 (Ethernet0) is down: keychain changed
R3(config)#interface ethernet0
R3(config-if)#ip authentication key-chain eigrp 100 EIGRP
R3(config-if)#ip authentication mode eigrp 100 md5
5d07h: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.23.2 (Ethernet0) is up:
As with RIPv2, the existing adjacency was torn down when one side was configured with authentication. If the key chain is correctly defined and applied on both sides, the adjacency will come back up. Always run show ip eigrp neighbor to make sure the adjacency is present. Learn the details of EIGRP key chains by configuring them on your home lab equipment, and you'll be more than ready for BSCI exam success!
In a previous tutorial, we saw how to configure RIPv2 packet authentication, with both clear-text and MD5 authentication schemes. EIGRP authentication is much the same, and has the text and MD5 authentication options as well. But EIGRP being EIGRP, the command just has to be a little more detailed!
As with RIPv2, the authentication mode must be agreed upon by the EIGRP neighbors. If one router's interface is configured for MD5 authentication and the remote router's interface is configured for text authentication, the adjacency will fail even if the two interfaces in question are configured to use the same password.
We'll now configure link authentication on the adjacency over an Ethernet segment. Below, you'll see how to configure a key chain called EIGRP on both routers, use key number 1, and use the key-string BSCI. Run show key chain on a router to see all key chains.
R2(config)#key chain EIGRP
R2(config-keychain)#key 1
R2(config-keychain-key)#key-string BSCI
R2#show key chain
Key-chain EIGRP:
key 1 -- text "BSCI"
accept lifetime (always valid) - (always valid) [valid now]
send lifetime (always valid) - (always valid) [valid now]
R3(config)#key chain EIGRP
R3(config-keychain)#key 1
R3(config-keychain-key)#key-string BSCI
R3#show key chain
Key-chain EIGRP:
key 1 -- text "BSCI"
accept lifetime (always valid) - (always valid) [valid now]
send lifetime (always valid) - (always valid) [valid now]
The EIGRP command to apply the key chain is a bit of a pain to remember, because the protocol and AS number is identified in the middle of the command, not the beginning. Also note that two commands are needed - one to name the key chain, another to define the authentication mode in use.
R2(config)#interface ethernet0
R2(config-if)#ip authentication key-chain eigrp 100 EIGRP
R2(config-if)#ip authentication mode eigrp 100 md5
5d07h: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.23.3 (Ethernet0) is down: keychain changed
R3(config)#interface ethernet0
R3(config-if)#ip authentication key-chain eigrp 100 EIGRP
R3(config-if)#ip authentication mode eigrp 100 md5
5d07h: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.23.2 (Ethernet0) is up:
As with RIPv2, the existing adjacency was torn down when one side was configured with authentication. If the key chain is correctly defined and applied on both sides, the adjacency will come back up. Always run show ip eigrp neighbor to make sure the adjacency is present. Learn the details of EIGRP key chains by configuring them on your home lab equipment, and you'll be more than ready for BSCI exam success!
Wednesday, December 24, 2008
Cisco CCNA Certification: The (Many) Different Kinds Of Switching
When you're studying for your CCNA exam, whether you're taking the Intro-ICND path or the single-exam path, you're quickly introduced to the fact that switching occurs at Layer 2 of the OSI model. No problem there, but then other terms involving switching are thrown in, and some of them can be more than a little confusing. What is "cell switching"? What is "circuit switching"? Most confusing of all, how can you have "packet switching"? Packets are found at Layer 3, but switching occurs at Layer 2. How can packets be switched?
Relax! As you'll see in this article, the terms aren't that hard to keep straight. Packet switching, for example, describes a protocol that divides a message into packets before they're sent. The packets are then sent individually, and may take different paths to the same destination. Once the packets arrive at the final destination, they are reassembled.
Frame switching follows the same process, but at a different layer of the OSI model. When the protocol runs at Layer 2 rather than Layer 3, the process is referred to as frame switching.
Cell switching also does much the same thing, but as the name implies, the device in use is a cell switch. Cell-switched packets are fixed in length. ATM is a popular cell-switching technology.
The process of circuit switching is just a bit different, in that the process of setting up the circuit itself is part of the process. The channel is set up between two parties, data is transmitted, and the channel is then torn down. The circuit-switching technology most familiar to CCNA candidates is ISDN.
Don't let these terms confuse you. The four different terms are describing much the same process. The main difference is that they are occurring at different levels of the OSI model, and using a different transport method to get the data where it needs to go.
Relax! As you'll see in this article, the terms aren't that hard to keep straight. Packet switching, for example, describes a protocol that divides a message into packets before they're sent. The packets are then sent individually, and may take different paths to the same destination. Once the packets arrive at the final destination, they are reassembled.
Frame switching follows the same process, but at a different layer of the OSI model. When the protocol runs at Layer 2 rather than Layer 3, the process is referred to as frame switching.
Cell switching also does much the same thing, but as the name implies, the device in use is a cell switch. Cell-switched packets are fixed in length. ATM is a popular cell-switching technology.
The process of circuit switching is just a bit different, in that the process of setting up the circuit itself is part of the process. The channel is set up between two parties, data is transmitted, and the channel is then torn down. The circuit-switching technology most familiar to CCNA candidates is ISDN.
Don't let these terms confuse you. The four different terms are describing much the same process. The main difference is that they are occurring at different levels of the OSI model, and using a different transport method to get the data where it needs to go.
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