One of the major new topics tested in the CCIE R&S Written Exam is Cisco's IP SLA feature. In response, I have updated your Written course with an IP SLA lesson. As you know, another reason you should master this technology is that it is a key ingredient in OER/PfR. This new lesson includes the following: Read More
The DHCP Information option (Option 82) is commonly used in metro or large enterprise deployments to provide additional information on “physical attachment” of the client. Option 82 is supposed to be used in distributed DHCP server/relay environment, where relays insert additional information to identify the client’s point of attachment. Read More
A question on GroupStudy gave me an idea for the short post dedicated to explaining the use of DHCP “import all” command. The command first appeared in IOS 12.2T. It allows importing certain DHCP information learned from some external source, such as another DHCP server. This is helpful in reducing the amount of configuration needed in large hub-and-spoke networks, where spokes use centralized servers (e.g. WINS, DNS, TFTP). Instead of configuring the repetitive settings in every spoke router,... Read More
Here is a small task that illustrates how combining a few technologies may result in interesting solution. Task: Configure R1 to send all logging messages to the remote server at the IP address "". Ensure secure (non-cleartext) and reliable (acknowledged) information delivery. DO NOT USE: 1) TCP as the transport protocol. 2) IPsec for encryption. 3) Any tunneling technology. Recent update: do not use BEEP. This seems to be ruled out by "don't use TCP", but worths being mentioned... Read More
Fragmented IPv4 traffic may cause you a lot of problems in real life. Not only it increases the load on router CPUs, but also impacts applications performance (e.g. TCP needs to re-send the whole packet on a single fragment loss). In addition to that, traffic fragmentation is used in numerous network attacks, allowing an attacker to bypass firewalls or IDSes in some situations. Due to all these reasons, you may want to avoid fragmentation at all and/or ensure your network is insulated from... Read More
More updates have been posted to the IP Services section of the CCIE Routing & Switching Lab Workbook Volume 1 Version 5.0.  The following topics are now available: Read More
For those of you eagerly awaiting updates to the new IEWB-RS Volume 1 Version 5.0 labs you’ll be happy to know that a partial release of the IP Services section is now posted. The following topics in IP Services are now available for download on the members site: Read More
Look at the following NAT scenario (thanks to Huan Pham on Groupstudy for the example). R2 is configured to translate R1 Loopback0 IP address to one of it’s own Loopback0 IP addresses: Read More
GLBP, an acronym for Gateway Load Balancing Protocol, is a virtual gateway protocol similar to HSRP and VRRP. However, unlike its little brothers, GLBP is capable of using multiple physical gateways at the same time. As we know, a single HSRP or VRRP group represents one virtual gateway, with single virtual IP and MAC addresses. Only one physical gateway in a standby/redundancy group is responsible for packet forwarding, others remain inactive in standby/backup state. If you have R1, R2, R3... Read More
Quite many people don't pay attention to the difference in handling packets on interfaces configured for NAT inside and outside. Here is an example to demonstrate how NAT "domains" interact with routing. Consider three routers connected in the following manner: Read More

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