Frame relay and split horizon for hub and spoke topology

http://ardenpackeer.com/routing-protocols/tutorial-troubleshooting-split-horizon-issues-part-1/

ΠΟΛΥ ΚΑΛΟ ANIMATION ΓΙΑ STP

http://www.cisco.com/image/gif/paws/10556/spanning_tree1.swf

cisco command reference (ios 12.3)

http://www.cisco.com/en/US/docs/ios/12_3/configfun/command/reference/fun_r.html

Configuring DNS

Router# show running-config
Building configuration...
Current configuration : 470 bytes!
version 12.2
service timestamps debug datetime msec
service timestamps log uptime
no service password-encryption!
hostname Router
!
!
ip subnet-zero
ip name-server 192.168.1.100
!--- Configures the IP address of the name server.
!--- Domain lookup is enabled by default.
!
!
interface Ethernet0
ip address 192.168.1.1 255.255.255.0
!
!
!--- Output Suppressed.
end

Cisco training tree

PPP/IP PACKET EXAMPLE

In the example shown the IP packet is encapsulated in a PPP frame including the flag sequence (7E), address (FF 03), protocol (00 21) and FCS (0B 81). In turn, the IP packet encapsulates a UDP message.

Example:7E FF 03 00 21 45 00 00 40 00 01 00 00 3C 11 E0 31 CE D9 8F 1F C7 B6 78 CB 04 63 00 35 00 2C AB DA 00 01 01 00 00 01 00 00 00 00 00 00 04 70 6F 70 64 02 69 78 06 6E 65 74 63 6F 6D 03 63 6F 6D 00 00 01 00 01 0B 81 7E
Start 7E
Address FF 03
SEP 00 21
IP Header 45 00 00 40 00 01 00 00 3C 11 E0 31 CE D9 8F 1F C7 B6 78 CB
Data 04 89 00 35 00 2C AB B4 00 01 01 00 00 01 00 00 00 00 00 00 04 70 6F 70 64 02 69 78 06 6E 65 74 63 6F 6D 03 63 6F 6D 00 00 01 00 01
FCS 0B 81
Stop 7E
IP Header
VER=4 IHL=5 TOS=0 TOL=64 ID=1 FLG=00 FRO=00 TTL=60 PRO=17 IP_SUM=E031 SRC=206.217.143.31. DEST=199.182.120.203. OPT=00000000

TCP/IP Packet Example

7E 21 45 00 00 4B 57 49 40 00 FA 06 85 77 C7 B6 78 0E CE D6 95 50 00 6E 04 9F 74 5B EE A2 59 9A 00 0E 50 18 24 00 E3 2A 00 00 2B 4F 4B 20 50 61 73 73 77 6F 72 64 20 72 65 71 75 69 72 65 64 20 66 6F 72 20 61 6C 65 78 75 72 2E 0D 0A 67 B2 7E
Start 7E
SEP 21
IP Header
45 00 00 4B 57 49 40 00 FA 06 85 77 C7 B6 78 0E CE D6 95 50
TCP Header 00 6E 04 9F 74 5B EE A2 59 9A 00 0E 50 18 24 00 E3 2A 00 00
Data 2B 4F 4B 20 50 61 73 73 77 6F 72 64 20 72 65 71 75 69 72 65 64 20 66 6F 72 20 61 6C 65 78 75 72 2E 0D 0A
FCS 67 B2
Stop 7E
TCP Header:
SRC_PORT=110
DEST_PORT=1183
EQ=745BEEA2
ACK=599A000E
DTO=5
FLG=18
WIND=9216
TCP_SUM=E32A
URP=0000 (No Options)
Data:+OK Password required for alexur\r\n
Control Flags
(FLG=18):FLG=00011000
Urgent Pointer URG=0
Acknowledgment ACK=1
Push Function PSH=1
Reset connection RST=0
Synchronization SYN=0
Finished data FIN=0
State = ACK-PSH