Cisco PPPoE configuration for BELL DSL Internet

vpdn enable
!
vpdn-group 1
! Default L2TP VPDN group
 accept-dialin
  protocol pppoe
!
interface FastEthernet0/0
 encapsulation dot1Q 102
 pppoe enable group global
 pppoe-client dial-pool-number 1
!
interface Dialer1
 description BELL Internet L3 PPPoE
 ip address negotiated
 ip nat outside
 ip virtual-reassembly
 encapsulation ppp
 ip tcp adjust-mss 1452
 load-interval 30
 dialer pool 1
 dialer-group 1
 ppp authentication pap callin
 ppp pap sent-username [username] password [password]
!
dialer-list 1 protocol ip permit

H.323 Basics


I’ve been studying for the CRMC specialization (Cisco Rich Media Communications) and am having a hard time keeping all of the various H.32x protocols straight.
In a nutshell, the H.323 standard provides the framework for audio, video and data communications over an IP network.
H.323 is a subset of the H.32x series of standards for video conferencing over different type of network media;
  • H.320 – ISDN
  • H.321 – Asynchronous Transfer Mode (ATM)
  • H.322 – local area networks which provide a guaranteed quality of service
  • H.323 – IP networks
  • H.324 – standard POTS lines
The H.323 specification actually consists of several protocols;
  • H.225 – provides registration, admission, and status (RAS) messages used between H.323 devices and the gatekeeper
  • H.235 – used for authentication and authorizing calls and for establishing encrypted channels for media of the calls.
  • H.239 – provides data sharing capabilities between video endpoints
  • H.245 -  control signaling used to exchange end-to-end control messages
There are three additional specialized protocols that are used for NAT transversal between endpoints and gatekeepers;
  • H.460.17 provides tunneling of call control signaling in Q.931 over TCP with the gatekeeper.
  • H.460.18 uses extra signaling in RAS with service control indication (SCI) and service control response (SCR) messages, so that inside devices open pinholes from inside for calls using RAS Facility messages.
  • H.460.19 uses empty RTP packets to open pinholes for incoming media.
Source.

13 Skills Every IT Pro Should Know

No matter which IT field you're working in, there are several skills that are useful for every IT professional to know. Here, seven experienced IT professionals working in the networking, programming, project management, and security fields share what they believe are the most important skills that every IT pro should know.

1. Programming

Even if your job doesn't require software development, it's useful to understand how applications are built because everything we do -- from following Twitter feeds to filling out expense forms -- is enabled by software. IT professionals with an academic background in computer science will likely have done some programming as part of their education. For others, there are many ways of learning programming.

Martin Harvey, PMP, managing consultant at Coroware, says: "The language I'd recommend learning would be any C-based language. It's a fairly common language that can be found in Microsoft and Java platforms, but it's not trivial. At the other end of the spectrum there are more interpretive languages such as Visual Basic and Python. It's easy to mess around with Visual Basic and Excel macros on your PC. You'll learn about the fundamentals of programming and the logic of how data is stored."

2. Learning from the book The Mythical Man-Month

Publisher Addison-Wesley Professional describes the book The Mythical Man-Month as "influential and timeless." Originally published in 1975, author Fred Brooks shares his experiences as project manager for IBM System/360 computer family and then for OS/360, its massive software system. Brooks made several mistakes including adding more workers to a project falling behind schedule, and underestimating the time it would take to complete a project. The book was republished in 1995 with new thoughts and advice from Brooks. Harvey says: "It's like 100 things your mother told you. I still made some of the mistakes after reading it. But if you read the book, maybe you won't make the mistakes or you will recognize that you are making them and know when to duck."

3. Understanding the basics of networking

"The network is how everything connects and every IT pro should know how that happens," says George Morton, a dual CCIE (Cisco Certified Internetwork Expert). Morton says IT pros should study and understand the following:

•Who is Cisco, Juniper, etc., and what do they offer. "Knowing that Dell makes switches won't get you to the top of the game," says Morton.
•TCP/IP and IP addressing
•Network Address Translation and Port Address Translation
•IPv6. "It is coming and the sooner you get on board the better for your career," Morton says.
•IP telephony: packet vs. switched
•What are routers, switches, and firewalls?
•Basic Access-List configuration for Cisco
•To be able to read a Cisco IOS running configuration; not so you administer the router but just understand what it is or isn't doing for you.
•Be familiar with guidance from the National Security Agency's Information Assurance for securing your network.

Morton recommends several books:
Cisco Networking Simplified
A first-class introduction to networking
Cisco IOS Cookbook, Second Edition
This book should be on every IT manager's desk. I use it to build some of the world's most complex networks. Why? It's easy to read, creates standards for the client, and covers almost everything I need.
JUNOS Cookbook and ScreenOS Cookbook

How to force Kerberos to use TCP instead of UDP in Windows

The Windows Kerberos authentication package is the default authentication package in Windows Server 2003, in Windows Server 2008, and in Windows Vista. It coexists with the NTLM challenge/response protocol and is used in instances where both a client and a server can negotiate Kerberos. Request for Comments (RFC) 1510 states that the client should send a User Datagram Protocol (UDP) datagram to port 88 at the IP address of the Key Distribution Center (KDC) when a client contacts the KDC. The KDC should respond with a reply datagram to the sending port at the sender's IP address. The RFC also states that UDP must be the first protocol that is tried.

Note. RFC 4120 now obsoletes RFC 1510. RFC 4120 specifies that a KDC must accept TCP requests and should listen for such requests on port 88 (decimal). By default, Windows Server 2008 and Windows Vista will try TCP first for Kerberos because the MaxPacketSize default is now 0. You can still use the MaxPacketSize registry value to override that behavior.

PBR and switching

Enabling Fast-Switched PBR

IP PBR can now be fast-switched. Prior to Cisco IOS Release 12.0, PBR could only be process-switched, which meant that on most platforms the switching rate was approximately 1000 to 10,000 packets per second. This speed was not fast enough for many applications. Users that need PBR to occur at faster speeds can now implement PBR without slowing down the router.

Fast-switched PBR supports all of the match commands and most of the set commands, with the following restrictions:

• The set ip default next-hop and set default interface commands are not supported.
• The set interface command is supported only over point-to-point links, unless a route cache entry exists using the same interface specified in the set interface command in the route map. Also, at the process level, the routing table is consulted to determine if the interface is on a reasonable path to the destination. During fast switching, the software does not make this check. Instead, if the packet matches, the software blindly forwards the packet to the specified interface.

PBR must be configured before you configure fast-switched PBR. Fast switching of PBR is disabled by default. To enable fast-switched PBR, use the following command in interface configuration mode:

Router(config-if)# ip route-cache policy
To display the cache entries in the policy route cache, use the show ip cache policy command. To display which route map is associated with which interface, use the show ip policy command.

Enabling CEF-Switched PBR

Beginning in Cisco IOS Release 12.0, PBR is supported in the Cisco Express Forwarding (CEF)switching path. CEF-switched PBR has better performance than fast-switched PBR and, therefore, is the optimal way to perform PBR on a router.

No special configuration is required to enable CEF-switched PBR. It is on by default as soon as you enable CEF and PBR on the router.

Note: The ip route-cache policy command is strictly for fast-switched PBR and, therefore, not required for CEF-switched PBR.

TCP MSS

The TCP MSS value specifies the maximum amount of TCP data in a single IP datagram that the local system can accept (reassemble). The IP datagram can be fragmented into multiple packets when sent. Theoretically, this value can be as large as 65495, but such a large value is never used. Typically, an end system uses the "outgoing interface MTU" minus 40 as its reported MSS. For example, an Ethernet MSS value is 1460 (1500 - 40 = 1460).

Source.

DHCP Snooping and IOS DHCP Server

If you have two crossconnected Cisco switches, for examples 3750, and first is DHCP server and second has ip dhcp snooping option enabled, and you have trouble with assigning an address with following error on switch which is DHCP server:

*Sep 25 19:00:02.159: DHCPD: inconsistent relay information.

*Sep 25 19:00:02.159: DHCPD: relay information option exists, but giaddr is zero.

There are two solution.
You should enable ip dhcp snooping on first switch or try entering this command on the switch:

switch(config)# no ip dhcp snooping information option

This will stop the switch from inserting relay information into the DHCPDISCOVER sent by the client. The switch tries to insert port and MAC address information into the packet by default, for situations like service providers.

Source.