Sep 302008
 

In Windows 2008 and Windows Vista, we can control the Multicast support, infact to be precise, the level of Multicast support and the version of the IGMP protocol that is supported from Windows Registry.

By default, Windows 2008 and Windows Vista supports IGMPv3 and fully pariticipates in IGMP where it can both send and receive IPv4 multicast packets.

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Sep 282008
 

IP Soure routing is an option which allows the source of a packet to specify the path that the packet will take, and what path return packets sent back to the source will take. Source routing is useful when the default route that a connection will take fails or is suboptimal for some reason, or for network diagnostic purposes. However, even more is a menace as poses a severe security issue where malicous users can exploit this feature to cause DoS attacks or even bypass LAN security rules in place.

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Sep 172008
 

A few days ago, we saw how to Enable/Disable Path MTU Discovery (PMTU Discovery) from the registry. Now, we shall go further and see how to Enable or Disable Path MTU Blackhole router detection in Windows 2008/Vista/2003/XP/2000 from Windows Registry. Path MTU Blackhole router detection is enabled by default so as the Path MTU Discovery.

A PMTU black hole router is a routing device which does not return ICMP Destination Unreachable messages when it needs to fragment an IPv4 packet that has the Don’t Fragment (DF) flag set. TCP depends on receiving these messages to perform PMTU discovery. With this feature enabled, TCP tries to send segments without the Don’t Fragment flag set if several retransmissions of a segment go unacknowledged. If the segment is then acknowledged, the TCP maximum segment size (MSS) for the connection is decreased and the Don’t Fragment flag is set for subsequent segments. Enabling PMTU black hole detection increases the maximum number of retransmissions that are performed for a given segment.

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Sep 112008
 

Path maximum transmission unit (PMTU) discovery is the process of discovering the maximum size of packet that can be sent across the network between two hosts without fragmentation (that is, without the packet being broken into multiple frames during transmission). By discovering the path MTU (PMTU) and limiting TCP segments to this size, TCP can eliminate fragmentation at routers along the path that connects networks with different MTUs. Fragmentation adversely affects TCP throughput and network congestion.

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Aug 212008
 


The Media Sensing feature in Windows 2000, Windows XP and later is used to detect whether the network media are in a link state. With Media Sense feature,  Windows senses a link state as UP or DOWN based on the link availability. When Windows detects a “down” state, it removes the bound protocols from that adapter until it is detected as “up” again.

Media Sensing feature is enabled by default in Windows except Windows Server 2003. However, in instances where you do not want Windows to sense link status (very unlikely) in which case, you can disable the Media Sensing feature from Windows Registry.

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