Tag Archives: TCP

1.1.f Explain UDP operations

1.1.f [i] Starvation

When TCP flows are combined with UDP flows within a single class and the class experiences congestion, TCP flows continually lower their transmission rates due to congestion control, potentially giving up their bandwidth to UDP flows that are oblivious to drops. This effect is called TCP starvation or UDP dominance.

Even if WRED is enabled on the class, the same behavior would be observed because WRED (for the most part) manages congestion only on TCP-based flows.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1169-1172).  . Kindle Edition.



1.1.e Explain TCP operations

1.1.e [vii] Options

A TCP segment consists of a segment header and a data section. The TCP header contains 10 mandatory fields, and an optional extension field.

Options have up to three fields:

1. Option-Kind (1 byte)

2. Option-Length (1 byte)

3. Option-Data (variable)

The ACL IP Options Selective Drop feature allows a router to filter IP options packets, thereby mitigating the effects of these packets on a router and downstream routers, and perform the following actions:

● Drop all IP options packets that it receives and prevent options from going deeper into the network. ● Ignore IP options packets destined for the router and treat them as if they had no IP options. The following example shows how to configure the router (and downstream routers) to drop all options packets that enter the network:

Router( config)# ip options drop

show ip traffic command can be used to verify the actual IP options drop statistics.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1157-1166).  . Kindle Edition.



1.1.e Explain TCP operations

1.1.e [vi] Global synchronization

Global synchronization happens when multiple TCP hosts reduce their transmission rates in response to packet dropping, then increase their transmission rates once again when the congestion is reduced.

WRED avoids the globalization problems that occur when tail drop is used as the congestion avoidance mechanism on the router.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1144-1147).  . Kindle Edition.



1.1.e Explain TCP operations

1.1.e [v] Bandwidth delay product

Bandwidth-delay product refers to the product (or multiplication) of a data link’s capacity (in bits per second) and its end-to-end delay (in seconds). The result, an amount of data measured in bits (or bytes), is equivalent to the maximum amount of data on the network circuit at any given time, i.e., data that has been transmitted but not yet acknowledged.

In wide area networks (WANs), where the end-to-end delay-bandwidth product becomes a significant factor, TCP uses the network buffers to sustain a steady-state throughput that matches the available network capacity.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 1138-1143).  . Kindle Edition.