Internet Routing I Flashcards
What is the goal of the Internet Protocol
To glue lower level networks together and establish connection between them
What is internet encapsulation??
Refers to the process of placing data packets into a series of protocol headers, including the source and destination IP addresses, to facilitate their transmission across the internet.
Is the internet protocol connectionless?
YES. it is datagram based. And the delivery is best-effort based
What is meant by best-effort delivery?
Packet are lost
They are delivered out of order
duplicate copies of a packet
they can be really delayed
What does these IP headers mean?
vers
hdrlen
DSCP ECN
Identification
Fragments offset
TTL
hdr checksum
Vers (Version): IP protocol version (IPv4 or IPv6).
Hdrlen (Header Length): Length of the IP header.
DSCP (Differentiated Services Code Point): Priority of the packet.
ECN (Explicit Congestion Notification): Indicates network congestion.
Identification: Unique identifier for reassembly.
Fragments Offset: Position of fragment in the original datagram.
TTL (Time to Live): Max hops before discarding.
Header Checksum: For header data integrity.
What is meant by this ?
- fragment necessary when MTU < size of datagram?
refers to a situation in computer networking where the Maximum Transmission Unit (MTU) of a network or link is smaller than the size of the datagram (packet) that needs to be transmitted.
Why do sender want to avoid fragmentation?
Because if a fragment is lost the WHOLE packet must be resent!
Why is the MF bit set in all IP fragments but the last one?
Because it indicates that there are more fragment coming. MF = more fragments
What does it mean when the DF flag is set?
DF = Dont Fragment, means exactly that. If fragmentation is required and DF bit is set then packet is not sent. Maybe target host does not have ability to reassemble.
Also note, if DF is set but MTS < size, the packet will be disregarded.
How does the IP distinguish between MF = 0, meaning last fragment and MF=0 meaning an unfragmented packet?
Last fragment has a non-zero offset field!
what IP address notation is this: 171.67.0.0/16
CIDR
what are the components of an IP adress 171.67.0.0/16 in CIDR notation?
The IP address itself is “171.67.0.0.”
The “/16” indicates the subnet mask. The first 16 bits of the IP address are the network portion and the remaining are for host addresses.
Network Address: 171.67.0.0
Subnet Mask: 255.255.0.0
How do we translate IP to Lower level address? (MAC)
USING ARP bitchhh
In IPv4: each network host has a lookup table (IP->link layer MAC addresses)
In IPv6: above + possible to encode MAC address in host part of IP
What does the Ineternet Control Message Protocol (ICMP) do?
It handles error messages, diagnostics, and control tasks in IP network
Name ICMP replies and explain what they mean/do
-Echo Reply: Indicates reachability.
-Destination Unreachable: Explains why a destination is unreachable.
-Time Exceeded: Notifies of TTL expiration to prevent looping.
-Redirect: Provides a new gateway for the destination.
-Parameter Problem: Reports header errors.
-Echo Request: Used for “Ping” requests to check reachability.
-Checksum Failed: Indicates a failed checksum in an ICMP message.
-Reassembly Failed: Signifies failed IP packet reassembly.
-Cannot Fragment: Informs that a packet cannot be fragmented further.
Define the Dynamic Host Cofiguration Protocol (DHCP)
- DHCP is a network protocol that automatically assigns IP addresses and other network configuration settings to devices in a TCP/IP network.
- It simplifies network management by dynamically allocating and managing IP addresses, subnet masks, gateways, and DNS server addresses.
- DHCP reduces manual IP configuration, making it easier to scale and manage networks efficiently.
What are the steps in DHCP leasing?
Request: Client broadcasts a request for an IP address.
Offer: DHCP server proposes an available IP address and settings.
Selection: Client selects an offer and requests it.
Acknowledgment: DHCP server assigns the IP address and provides settings.
Lease: Client can use the IP address for a specified duration.
Renewal: Client can request a lease renewal as it nears expiration.
Lease Rebinding:
If the DHCP client cannot reach the original DHCP server for lease renewal, it will attempt to renew with any DHCP server on the network, known as the lease rebinding process. This provides a safety net in case the original server is unavailable.
Release: Client releases the IP address when disconnecting or leaving the network.
DHCP leasing automates IP address allocation and management in networks
what is a DHCP scope
refers to a range of IPs that a DHCP server can rent out.
TYhere are also exclusions, reservations and Load balancing involved within DHCP scope
What is the difference between routing and forwarding?
Routing: determines the optimal path for data between networks.
Forwarding: implements the immediate delivery of data based on routing decisions.
Layer: Routing primarily occurs at Layer 3 (Network Layer), while forwarding can occur at both Layers 2 (Data Link Layer) and 3.
Function: Routing selects the best route, considering destination IP addresses and network topology. Forwarding handles the actual transmission of data based on those routing decisions.
Scope: Routing is essential for interconnecting networks, while forwarding is concerned with local and inter-network delivery.
What is an Intra-Domain Routing Protocols: (Interior Gateway Protocol - IGP), and give me examples of such protocol
These are routing protocols used within a single autonomous system or network.
- Open Shortest Path First (OSPF): This is a link-state routing protocol used to determine the best path for routing within a single network
- RIP (Routing Information Protocol): This is a distance-vector routing protocol that calculates the best path based on the number of hops.
What is an Inter-domain routing protocols: exterior gateway protocol (EGP) and give me an example of such?
These are routing protocols used for communication between different autonomous systems or networks.
- Border Gateway Protocol v4 (BGP): This is a path vector routing protocol used to communicate between autonomous systems, listing possible paths for data to follow.
What are the two main rules for entries in a forwarding table?
Destination addr and next-hop information
Entries in a forwarding table must either have a prefix mapped to the next hop or know the default route for unknown prefixes.
What principle is used to determine the best route when multiple prefixes match a destination address?
Routing uses the “longest prefix match” principle, where the most specific (longest) matching prefix is chosen.
How do core routers in a network differ from other routers in terms of routing knowledge?
Core routers typically know about all available routes and don’t rely on a default route. They have comprehensive routing information.
What is the role of Autonomous Systems (AS) in internet routing?
Independently managed network domains that use interior gateway protocols (IGPs) to route traffic within their networks and exterior gateway protocols (EGPs) like BGP to exchange routing information with other ASes, enabling efficient and reliable global internet communication.
What is the two-level hierarchy of route propagation in the context of ASes (Autonomous Systems)?
Routing within an AS is managed using an interior gateway protocol (IGP), where each AS selects its own standards and policies. Routing between different ASes is governed by an exterior gateway protocol (EGP), which is an Internet-wide standard.
What is the benefit of the internet being divided into ASes?
- Scalability: Manageable growth in independently administered ASes.
- Administrative Autonomy: Tailored routing policies per AS.
- Reduced Complexity: Simplified routing within and between ASes.
-Isolation & Security: Contain issues within ASes, enhancing security.
-Performance Optimization: Localized routing for improved performance.
-Interconnection Flexibility: Choose network connections and peering relationships.
What types of traffic are there in relation to an AS?
Local traffic – packets with source or destination in local AS
Transit traffic – passes through an AS
Stub AS
Connects to only a single other AS
Multihomed AS
Connects to multiple ASes
Carries no transit traffic
Transit AS
Connects to multiple ASes and carries transit traffic
What is the difference between a switch and a Router?
Swith: operates on Link layer and forwards datagram wihtin LANS
Router: forwards packets between LANS and operates on Network layer
What values does a Swithes MAC table hold?
Mac address to port on switch
What is intra-domain routing vs inter-domain routing ?
Intra-domain routing refers to routing within a single network or administrative domain, while inter-domain routing involves routing traffic between different network domains or autonomous systems on the internet.
What does the host portion of an IP specify?
The individual device within the network
Whas is aggregation in terms of addresses?
A process that groups IP addresses together for more efficient routing.
Why does addresses need to be translated?
It’s due to the distinction between Layer 2 (link) addresses and Layer 3 (network) adrresses.
Which OSI level does ARP operate at?
Layer 2 (datalink layer)
Where are ICMP messages carried?
They are carried within IP packets
Define Tracert (traceroute)
command-line tool that traces the route that packets take from your computer to a destination server
When do you want to use ping vs tractert?
Ping: when you want to quickly check if a host is responsive and measure basic latency.
Tracert: when you want to troubleshoot network path issues, identify routing problems, or analyze network bottlenecks.
Lists up the steps of a DHCP leasing proccess
DORALRRR
Discorvery
Offer
Request
Ack
Lease Time
Renewal
Rebind
Release
How is loadbalancing connected to DHCP?
In larger networks w/ multiple DHCP servers, load balancing can be implemented to distribute the DHCP workload evenly between servers
