October 15, 2013
If you are going to setup a LAN with redundant paths, it is important that STP is running. If not you will be opening yourself up to these few problems
- Broadcast Storms
- MAC Table instability
- Multiple frame transmission
While the issue of broadcast storms may seem obvious, the other two may not be the things you think about at all. In the case of MAC table instability your switches will experience frequent updates to their MAC tables with wrong entires, from the looped frames which are being sent around the LAN.
The second issue of Multiple frame transmission can be somewhat, a disastrous side affect of not running STP. Duplicate copies of the looping frame can end up at the end host, in turn completely confusing it, resulting in discarded frames.
Luckily though on CISCO switches STP is on by DEFAULT
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Networking, Protocols, Switches, Troubleshoot | Tagged: broadcast storms, ccna, ccna exam, cisco, cisco switching, computer networks, frames, icnd2, icnd2 exam, it networking, mac, MAC table, networking, stp, switches | 
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Posted by Josh Gahan
May 19, 2013
| Layer |
Protocol |
| Application |
HTTP, POP3, SMTP |
| Transport |
TCP, UDP |
| Internet |
IP, IPv6 |
| Data-Link |
MAC |
| Physical |
Ethernet, PPP, T/1 |
Leave a Comment » | Networking, Protocols, TCP/IP Model | Tagged: application, ccent, ccna, dat-link, ethernet, hhtp, internet, ip, ipv6, mac, mac address, physical, pop3, ppp, protocols, smtp, t/1, TCP, tcpip, transport, UDP | Permalink
Posted by Josh Gahan
April 28, 2013
Switches examine the source MAC address of the received frame, switches can take a few possible options if it discovers that the incoming MAC address on that port is NOT SECURE.
- shutdown (the switch shuts down the port and sends a log message and drops the frame/s , also the interface status will read err-disabled you have to run a no shutdown to open the port again) ON BY DEFAULT
- restrict (drops the frames and transmits a log message but does not shutdown the port)
- protect (only drops the frames)
When configuring Port security and the source MAC address is unknown switchport port-security mac-address sticky can be used and the switch will use the first mac address learned as the Secure MAC address
Leave a Comment » | Networking, Security, Switches | Tagged: advice, ccent, ccent exam, ccna, ccna exam, cent, cisco, cisco hardware, cisco ios, cisco switches, cisco switching, did you know, err-disabled, hints n tips, information technology, iOS, ios commands, it, it security, mac, mac address, networking, packet, port security, protocol, router, security, switches, TCP, transmission control protocol, UDP | Permalink
Posted by Josh Gahan