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37 Cards in this Set
- Front
- Back
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What is an MTU?
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Maximum Transmission Unit. It is the maximum size of the PDU each medium can transport.
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What is it called when an intermediary device has to split a packet to fit it on a medium with a smaller MTU?
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Fragmenting
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What is the process of determining an MTU's size?
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The data link layer passes the MTU value to the network layer. The network layer then decides how big the packet should be.
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An IPv4 packet has two parts. What are they?
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IP header - Identifies the packet characteristics.
Payload - Contains Layer 4 segment info and the actual data. |
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What is DS?
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Differentiated Services. It determines the priority of each packet.
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What are the first six bits of Differentiated Services reserved for?
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Differentiated Services Code Point. This determines the quality of service.
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What are the last two bits of Differentiated Services reserved for?
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Explicit congestion notification. This can be used to prevent lost packets during heavy network congestion.
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What does the version in an IP packet depict?
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...How about the version? Either 4 or 6 (0100 or 0110 respectively).
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What is TTL?
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Time to live. 8 bit binary limit to the lifetime of a packet. It's specified in seconds, but is commonly referred to as a hop count. If it is exceeded, the router drops the packet and sends an ICMP message stating "Time Exceeded" to the source.
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What does the protocol header include?
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It indicates the payload type. The most common are ICMP (0x01), TCP (0x06) and UDP (0x11).
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What are the two most commonly referenced fields in an IPv4 header?
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Source and destination IP address
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What is IHL?
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Internet Header Length. Identifies the number of 32 bit words in the header. Minimum value is 5 and maximum is 15. It varies due to options and padding.
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What does the total length header field do?
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Also known as packet length, it defines the entire packet size in bytes. The minimum is 20 bytes and the maximum is 65,535.
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What is a header checksum?
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It is used for error checking in an IP header.
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What is an identification field used for?
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Used when a packet is fragmented, it uniquely identifies the fragment of the original IP packet.
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What is the flags header used for?
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In fragmentation, it's used to identify how the packet is fragmented.
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What is a fragment offset?
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It identifies the order in which to place the packet fragment when restructuring.
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What is NAT?
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Network Address Translation. It was a feeble attempt to preserve IPv4 addresses. Multiple devices on an internal network share a common public IP address.
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Why is IPv6 awesome?
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- Fewer header fields improves packet handling
- Provides scalability options for the future - More secure because it natively supports authentication and privacy capabilities - WAAAAY more IP addresses - No more NAT |
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What is the Traffic Class field?
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IPv6's equivalent to Differentiated Services. It also contains Differentiated Services Code Point and Explicit Network Congestion.
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What is a Flow Label header for?
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IPv6. Special service for real times apps. It can inform routers and switches to maintain the same path for the packet flow so packets aren't reordered.
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What is the payload length field for?
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IPv6's solution to the total length field. It defines the entire size of the IPv6 packet.
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What's the next header field for?
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IPv6's equivalent to the protocol field. It indicates the type of data payload the packet carries.
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What's the hop limit field for?
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Exactly what it sounds like. It counts the number of router hops a packet makes. It replaces IPv4's TTL.
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What is EH?
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Extension headers. Used in IPv6, they are optional and place between the header and the payload. Used in fragmentation, security, mobility and so on.
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What is a routing table and where is it stored?
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It stored route information about the directly connected network as well as entries about remote networks it has contacted previously. It is utilized to determine the best path to take to reach its destination. It is stored in the RAM of a router.
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How do you display a PC's local routing table?
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route print or netstat -r
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What is the local default route?
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Indicates the route packets must take to reach a remote network (cross the default gateway).
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What is an interface list in a routing table?
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Lists the MAC addresses and assigned interface number of every network device installed on the PC.
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What does an IPv4/IPv6 route table contain?
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A list of all the known IPv4/IPv6 routes on the local segment.
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What is the Network Destination column for in a PC's routing table?
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It lists reachable networks.
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What is the Netmask column for in a PC's routing table?
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Lists subnet masks that inform the host which part of network a host is on.
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What is the Gateway column for in a PC's routing table?
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Lists address used by the local PC to get to remote destinations. If a destination is direction reachable, it'll say 'on-link'.
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What is the interface column for in a PC's routing table?
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It lists the address of the physical interface used to send the packet to the gateway.
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What is the metric column used for in a PC's routing table?
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It lists the cost of each route. It is used to determine the best route for a packet to take.
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What is 0.0.0.0 in a routing table?
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Local default route. It specifies that all packets with a destination that doesn't match an address in the routing table are forwarded to the gateway.
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What is 255.255.255.255 representing on a routing table?
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Represents the limited broadcast IP address values for use through either the loopback or host IP. Can be used to find DHCP servers before local IP is determined.
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