Question

RFC 791 describes the Internet Protocol and includes two options for source routing. Describe three disadvantages of using IP source route options compared to using MPLS for explicit routing. (Hint: The IP header including options may be at most 15 words long.)

Short answer

Disadvantages include limited header space, increased processing overhead, and higher vulnerability to security exploits.

Step-by-step solution

- Understand Source Routing in IP

Source routing is a technique where the sender of a packet specifies the route that the packet should take through the network. RFC 791 describes this in terms of options in the IP header.

- Review the Constraints of IP

The IP header, including options, may only be at most 15 words long (with a word being 4 bytes). This imposes a significant limitation on the amount of routing information that can be included.

- Compare to MPLS

Multiprotocol Label Switching (MPLS) is a more modern technique for explicit routing. It uses labels rather than IP addresses to forward packets, enabling more complex routing without the same header length constraint.

- Identify First Disadvantage

The first disadvantage of IP source routing is the limited space in the IP header. With only 15 words available, the amount of routing information is heavily restricted, limiting the number of hops or complexity of paths that can be specified.

- Identify Second Disadvantage

The second disadvantage is processing overhead. Each router must examine the source route option in the IP header, which imposes additional processing burden compared to MPLS where routers simply swap labels.

- Identify Third Disadvantage

The third disadvantage is security. IP source routing can be exploited by attackers to bypass network security measures. MPLS, by contrast, does not expose explicit routing information in the same way.

Key concepts

Internet Protocol (IP)

The Internet Protocol (IP) is fundamental to how data travels across networks. It is like a postal system for the internet, ensuring that data packets reach their destination. IP works by assigning an address to each device on the network, known as an IP address. There are two versions: IPv4 and IPv6. IPv4 is older and uses 32-bit addresses, while IPv6 uses 128-bit addresses, allowing for a vast number of unique addresses. IP is responsible for slicing data into packets, adding addressing information, and routing these packets from the source to the destination. However, IP itself doesn't ensure the reliability of the data transfer—that's the job of higher-level protocols like TCP.

Source Routing

Source routing is a method where the sender of a packet dictates the exact route that the packet should take through the network. This is done by including a list of network addresses in the packet's header. The main advantage of source routing is its control over the route and the ability to avoid congested paths. However, the method has some notable downsides:

• Limited Space: The IP header can contain only 15 words, heavily restricting the amount of routing information.
• Increased Processing Overhead: Each router must read and process the source routing information, causing delays.
• Security Risks: Attackers can exploit source routing to bypass security measures, leading to potential breaches.

These limitations make source routing less appealing in modern networking compared to alternatives like MPLS.

Multiprotocol Label Switching (MPLS)

Multiprotocol Label Switching (MPLS) is an advanced technique for directing data across a network. Unlike IP, which uses addresses to route packets, MPLS uses labels. Each packet is assigned a label at the entry point of the network, and routers forward packets based on these labels. This method significantly speeds up the routing process and simplifies the network design. MPLS offers several advantages:

• Efficient Routing: By simplifying packet forwarding through label swapping, MPLS reduces latency and speeds up network traffic.
• Scalability: MPLS can handle complex routing decisions without cumbersome IP header information.
• Security: MPLS hides routing details from potential attackers, mitigating certain security risks inherent in IP source routing.

These benefits make MPLS an attractive choice for modern enterprise networks and service providers.

Routing Constraints

Routing constraints are limitations and rules that affect how data can be routed through a network. Several factors influence routing decisions:

• Header Size: IP headers have a limited size, which restricts the amount of routing information that can be included, specifically in options like source routing.
• Processing Capabilities: Routers have finite processing power. Complex routing decisions, like those required by source routing, can burden these devices.
• Security Policies: Networks implement security measures that constrain routing paths to prevent unauthorized access. Source routing can conflict with these policies.
• Network Topology: The physical and logical layout of the network impacts routing paths. Path length, bandwidth, and reliability considerations also act as constraints.

These constraints necessitate the use of efficient and secure methods like MPLS for effective network management.

Network Security

Network security is a critical aspect of designing and managing a network. It encompasses measures taken to protect the integrity, confidentiality, and availability of data as it traverses the network. Significant considerations include:

• Access Controls: Restricting who can access and modify network resources.
• Encryption: Protecting data from eavesdropping and tampering during transmission.
• Monitoring and Intrusion Detection: Detecting and responding to unauthorized activities.
• Firewall and VPN: Configuring firewalls to block malicious traffic and using VPNs to secure communications.

With IP source routing, there’s a risk of attackers manipulating the route, potentially bypassing security measures. MPLS offers a more robust approach where routing information is obscured, minimizing these risks.

Processing Overhead

Processing overhead refers to the additional computational burden placed on network devices like routers. In the context of routing:

• IP Source Routing: Each router must read and process the source routing information in the IP header. This increases the processing load and can lead to inefficiencies, especially in high-traffic networks.
• MPLS: Routers forward data based on simple label swapping, which is significantly more efficient. This reduces the processing time required per packet and lowers latency.

Reducing processing overhead is vital for maintaining high-speed network performance and scalability. By minimizing the complexity of routing decisions, MPLS ensures that routers can handle large volumes of traffic efficiently.