Networking Tips Tricks

Technical details Schema of a typical DHCP session DHCP uses the same two IANA assigned ports as BOOTP: 67/udp for the server side, and 68/udp for the client side. DHCP operations fall into four basic phases. These phases are IP lease request, IP lease offer, IP lease selection, and IP lease acknowledgement. After the client obtained an IP address, the client may start an address resolution query to prevent IP conflicts caused by address poll overlapping of DHCP servers. DHCP discovery The client broadcasts on the local physical subnet to find available servers. Network administrators can configure a local router to forward DHCP packets to a DHCP server on a different subnet. This client-implementation creates a UDP packet with the broadcast destination of 255.255.255.255 or subnet broadcast address. A client can also request its last-known IP address (in the example below, 192.168.1.100). If the client is still in a network where this IP is valid, the server might grant the request. O...

Requirement Cisco Command Enable debug for RIP debug ip rip Enable summary IGRP debug information debug ip igrp events Enable detailed IGRP debug information debug ip igrp transactions Debug IPX RIP debug ipx routing activity Debug IPX SAP debug IPX SAP Enable debug for CHAP or PAP debug ppp authentication Switch all debugging off no debug all undebug all

Requirement Cisco Command Save the current configuration from DRAM to NVRAM copy running-config startup-config Merge NVRAM configuration to DRAM copy startup-config running-config Copy DRAM configuration to a TFTP server copy runing-config tftp Merge TFTP configuration with current router configuration held in DRAM copy tftp runing-config Backup the IOS onto a TFTP server copy flash tftp Upgrade the router IOS from a TFTP server copy tftp flash

Requirement Cisco Command Enter privileged mode Enable Return to user mode from privileged disable Exit Router Logout or exit or quit Recall last command up arrow or Recall next command down arrow or Suspend or abort and 6 then x Complete Command TAB

Requirement Cisco Command View version information show version View current configuration (DRAM) show running-config View startup configuration (NVRAM) show startup-config Show IOS file and flash space show flash Shows all logs that the router has in its memory show log View the interface status of interface e0 show interface e0 Overview all interfaces on the router show ip interfaces brief View type of serial cable on s0 show controllers 0 (note the space between the 's' and the '0') Display a summary of connected cdp devices show cdp neighbor Display detailed information on all devices show cdp entry Display current routing protocols show ip protocols Display IP routing table show ip route Display access lists, this includes the number of displayed matches show access-lists Check the router can see the ISDN switch show isdn status Check a Frame Relay PVC connections show frame-relay pvc show lmi traffic stats show frame-relay lmi Display the frame inverse ARP table s...

Requirement *Cisco Command* Set a console password to cisco Router(config)#*line con 0* Router(config-line)#*login* Router(config-line)#*password cisco* Set a telnet password Router(config)#*line vty 0 4* Router(config-line)#*login* Router(config-line)#*password cisco* Stop console timing out Router(config)#*line con 0* Router(config-line)#*exec-timeout 0 0* Set the enable password to cisco Router(config)#*enable password cisco* Set the enable secret password to peter. This password overrides the enable password and is encypted within the config file Router(config)#*enable secret peter* Enable an interface Router(config-if)#*no shutdown* To disable an interface Router(config-if)#*shutdown* Set the clock rate for a router with a DCE cable to 64K Router(config-if)*clock rate 64000* Set a logical bandwidth assignment of 64K to the serial interface Router(config-if)*bandwidth 64* *Note that the zeroes are not missing* To add an IP address to a interface Router(config-if)#*ip addr 10.1.1.1 ...

*Understanding Patches* When vendors become aware of vulnerabilities in their products, they often issue patches to fix the problem. Make sure to apply relevant patches to your computer as soon as possible so that your system is protected. *What are patches?* Similar to the way fabric patches are used to repair holes in clothing, software patches repair holes in software programs. Patches are updates that fix a particular problem or vulnerability within a program. Sometimes, instead of just releasing a patch, vendors will release an upgraded version of their software, although they may refer to the upgrade as a patch. *How do you find out what patches you need to install?* When patches are available, vendors usually put them on their websites for users to download. It is important to install a patch as soon as possible to protect your computer from attackers who would take advantage of the vulnerability. Attackers may target vulnerabilities for months or even years after patches are av...