http://gallery.rrod.net/dokuwiki/ 2012-05-21T01:48:34+01:00 http://gallery.rrod.net/dokuwiki/ http://gallery.rrod.net/dokuwiki/lib/tpl/default/images/favicon.ico text/html 2011-10-09T15:27:05+01:00 Jarrod Lowe http://gallery.rrod.net/dokuwiki/doku.php?id=checking_layer_2&rev=1318170425&do=diff This page references the Simple Network 1 sample network. If a system is unable to communicate with an IP address that should be on an attached network; the issue may be to do with the Layer 2 connectivity: * Is the Layer 2 link physically OK? * Are you connected to the device and port you think you are? * Are you in the correct VLAN (or other domain)? * Are you being filtered/firewalled? * If you have multiple ports, are they wired the right way round? * If there are redundant pat… text/html 2011-10-09T14:28:26+01:00 Jarrod Lowe http://gallery.rrod.net/dokuwiki/doku.php?id=defs:simple_network_1&rev=1318166906&do=diff This is a very simple network. It has two nodes, one of which is a host, and the other of which is a router. It also has a switch. TODO: Diagrams The host is: * called host1.example.com, * has a single physical interface called eth0, * eth0 is a copper gigabit ethernet, with the MAC address fe-00-bb-bb-bb-bb, * eth0 is connected to the switch on its physical interface 1 * has the IPv4 address 192.0.2.100/24 on its eth0 interface, * has a static default IPv4 route (0.0.0.0/0) via … text/html 2011-09-13T14:50:18+01:00 Jarrod Lowe http://gallery.rrod.net/dokuwiki/doku.php?id=failed_redundant_paths_at_layer_3&rev=1315921818&do=diff As packets pass over the Internet (or a large internal network) between source and destination networks; they may end up passing through multiple paths -- that is not every packet necessarily ends up going the same way. If a path fails, the equipment around it should automatically stop using it -- however, sometimes this doesn't happen. text/html 2011-09-13T14:36:08+01:00 Jarrod Lowe http://gallery.rrod.net/dokuwiki/doku.php?id=start&rev=1315920968&do=diff A collected experience. Introduction * Target Audience * Definitions -- Including standard networks referenced throughout the book * Tools Unsorted * Checking Layer 2 * Failed Redundant Paths at Layer 3 text/html 2011-09-10T15:56:54+01:00 Jarrod Lowe http://gallery.rrod.net/dokuwiki/doku.php?id=tools:tcpdump&rev=1315666614&do=diff tcpdump will show packets going in or out (or in some cases past) an interface. Useful Flags * -n: Turn off DNS lookups. You will almost always want this, as it delays the printing of packets. This can leave you thinking no packet arrived, when in fact it did, but DNS was slow * -c n: Run for n packets and stop. You should always use this flag when running tcpdump on a remote machine. If it ends up displaying a lot of packets you can spend a long time trying to hammer ^C down the link. Thi… text/html 2011-09-10T15:56:10+01:00 Jarrod Lowe http://gallery.rrod.net/dokuwiki/doku.php?id=defs:start&rev=1315666570&do=diff Standard Networks These are networks that we will refer to throughout the book * Simple Network 1 * Simple Network 1 --- A Host and a Router and a Switch * Simple Network 1 with Redundant Routers -- VRRP or HSRP Terms * interface: The Operating System side of a network device. This refers to its representation inside the kernel, and what you refer to with commands. * port: The Physical side of a network device. The actual plug in the machine. * physical interface: An interface… text/html 2011-09-10T15:55:58+01:00 Jarrod Lowe http://gallery.rrod.net/dokuwiki/doku.php?id=target_audience&rev=1315666558&do=diff This book is targeted at people with a solid understanding of TCP/IP and IP routing already. It will not teach you about netmasks or ports. The examples in this book usually assume Linux, unless otherwise stated. However, the principles should carry over to other Operating Systems.