BGP (Border Gateway Protocol) uses a multi-step decision process to select the best route among multiple paths. It does not use SPF or simple metrics like hop count .

Key BGP selection criteria include:

Local preference

AS path length

Origin type

MED (Multi-Exit Discriminator)

eBGP over iBGP

IGP metric to next hop

Option C is correct – BGP evaluates multiple attributes for route selection.

A P router (Provider router) is located in the core of the service provider’s network . Its functions include:

Forwarding MPLS-labeled packets between PE routers .

Not interacting directly with customer routes or routing instances.

Having no knowledge of VPN routing or customer-specific services .

Option C is correct – P routers sit in the MPLS core , isolated from customer edge.

ICMP (Internet Control Message Protocol) is used for network diagnostics and error messaging. Key uses include:

Ping (Echo Request/Reply) – tests end-to-end connectivity ✔

Traceroute – uses ICMP time exceeded messages to identify hops ✔

Error reporting – returns various error types with different codes ✔

However, ICMP does not re-route traffic . If a destination is unreachable, ICMP reports the error back to the sender; it doesn’t instruct routers to re-route.

Option D is FALSE – ICMP does not perform routing .

The DHCP client/server exchange follows a specific four-step sequence known as DORA :

Discover – Client broadcasts to find available DHCP servers.

Offer – DHCP server responds with an IP address offer.

Request – Client requests the offered IP.

Acknowledgement – Server confirms the lease.

This ensures dynamic IP configuration and is used in enterprise and home networks.

A /31 subnet in IPv4 provides exactly two IP addresses (e.g., 192.168.1.0/31 → usable: 192.168.1.0 and 192.168.1.1). Traditionally, these would represent a network address and a broadcast address , but RFC 3021 redefines /31 subnets for point-to-point links , such as router-to-router connections.

In a /31 subnet:

Broadcast address is not used .

Both IPs are treated as usable host addresses .

It's ideal for point-to-point links , saving address space.

This is widely supported and standardized in Nokia IP and routing platforms .

A Virtual Local Area Network (VLAN) is a logical separation of devices at Layer 2 , even if those devices are connected to the same physical switch. Each VLAN forms its own broadcast domain , and traffic cannot cross from one VLAN to another without Layer 3 routing .

Option A is incorrect – devices on the same switch but in different VLANs still cannot communicate directly.

Option B is incorrect – VLANs explicitly create separate broadcast domains .

Option D is technically incorrect – communication is possible with the right setup.

Option C is correct – to enable communication between different VLANs, a router or a Layer 3 switch with inter-VLAN routing capability is required.

This process is called inter-VLAN routing , and it's a fundamental task in enterprise networks using VLANs.

VPWS (Virtual Private Wire Service) on Nokia 7750 SR:

Emulates a Layer 2 point-to-point connection.

Does not require MAC learning , unlike VPLS.

Uses MPLS encapsulation , not IP datagrams for transport.

Option D is FALSE – VPWS uses MPLS labels , not IP encapsulation.