SHARIFUL's TECH BLOG

The other day; I was testing how my ISP is protecting itself from customer exploitation. Normally I directly connect my router to the network cable provided by ISP. This time around I have connected a switch to the network cable from the  ISP. Then I have configured the switch port (ISP connection) to an access VLAN and also configured 2 other switch ports to the same vlan. Then I have connected 2 routers and expecting they will be assigned 2 IP addresses (1 for each router). To my surprise only one of the router was getting dynamically assigned IP adress from the ISP. The second router was not getting any IP adress at all. I even went further to set an static IP adress (from ISP network) to the second router. Another surprise - even with static IP assignment, that router could not even ping the ISP's gateway. That got me thinking - how the ISP is protecting itself from such customer exploitation in the first place. Disclaimer - This is just a story to show the readers how th...

The other day, I was looking at the arp table entry for my home router and found a funny thing going on - $ show arp Address                 HWtype    HWaddress              Iface 10.10.10.1              ether        04-96-AF-EF-C6-53    eth0 10.10.10.10            ether        04-96-AF-EF-C6-53    eth0 Above arp table is an example hiding the actual IP addresses and MAC addresses. Here my IP address is let's say - 10.10.10.50/24 and GW is 10.10.10.1 . Now the question comes why another subscriber of the ISP in the same subnet (10.10.10.10) also have same mac address as my GW (04-96-AF-EF-C6-53). We are in the same IP network/VLAN (ISP definitely configured those), but my router cannot see the actual MAC address of other devices in the network. The reason is that my ISP is i...