Network+ 6 Flashcards
BOOTP : When a device needed to obtain IP address information, a BOOTP broadcast would be sent out from the device needing an IP address. If a BOOTP server (BOOTPS) received the broadcast, it could match the source MAC address in the received frame (the MAC address from the device wanting to obtain an IP address) with a corresponding IP address in a database stored on the BOOTP server. The BOOTPS would then respond to the requesting client with IP address information. Because BOOTP requests were based on broadcasts, by default, a BOOTP request could not propagate beyond a device’s local subnet. However, most enterprise-class routers can be configured to forward selected broadcast types, including BOOTP broadcasts.
BOOTP
IPv6 : Simplified header: IPv4 header uses 12 fields. IPv6 header uses eight fields. No broadcasts. No fragmentation (performs MTU discovery for each session). Can coexist with IPv4 during a transition. Dual stack (running IPv4 and IPv6 simultaneously on a network interface or device). IPv6 over IPv4 (tunneling IPv6 over an IPv4 tunnel). 128 bits in an IPv6 address.
IPv6
Using Teredo tunneling, an IPv6 host could provide IPv6 connectivity even when the host is directly connected to an IPv4-only network. Miredo is a client that can be used to implement the Teredo protocol and is included in many versions of Linux. IPv6/IPv4 tunneling is often referred to as 6-to-4 or 4-to-6 tunneling, depending on which protocol is being tunneled (IPv4 or IPv6).
*** With anycast, a single IPv6 address is assigned to multiple devices. It is a one-to-nearest (from the perspective of a router’s routing table) communication flow.
Teredo Tunneling
Neighbor Discovery Protocol is hugely important in IPv6. It defines five ICMPv6 packet types for important jobs:
Router Solicitation: Hosts inquire with Router Solicitation messages to locate routers on an attached link.
Router Advertisement: Routers advertise their presence together with various link and Internet parameters, either periodically or in response to a Router Solicitation message.
Neighbor Solicitation: Neighbor solicitations are used by nodes to determine the link layer address of a neighbor, or to verify that a neighbor is still reachable via a cached link layer address.
Neighbor Advertisement: Neighbor advertisements are used by nodes to respond to a Neighbor Solicitation message.
Redirect: Routers may inform hosts of a better first-hop router for a destination.
NDP
An IP header contains a Time To Live (TTL) field, which is decremented once for each router hop. If the value in the TTL field is reduced to 0, the router discards the frame and sends a “time exceeded” Internet Control Message Protocol (ICMP) message back to the source.
*** Static route means the router is configured to send traffic to the specific destination in the preconfigured direction and Dynamic route that uses a routing protocol such as OSPF to determine the traffic direction.
TTL
Administrative distance of Routing Protocols : Directly Connected Network = 1, Statically configured network = 1, EIGRP = 90, OSPF = 110, RIP = 120, External EIGRP = 170, Unknown of unbelievable = 255 (considered to be unreachable). Lower metrics are preferred over higher metrics. If a routing protocol knows of more than one route to reach a destination network and those routes have equal metrics, some routing protocols support load balancing across equal-cost paths. EIGRP can even be configured to load-balance across unequal-cost paths.
Routing Protocols
Interior Gateway Protocols (IGPs) operate within an autonomous system, where an autonomous system is a network under a single administrative control. Conversely, Exterior Gateway Protocols (EGPs) operate between autonomous systems. Within those autonomous systems, an IGP is used to exchange routing information. An EGP (typically, Border Gateway Protocol) is used to exchange routing information between the service provider’s autonomous system and each of the other autonomous systems.
IGP/EGP
A distance-vector routing protocol sends a full copy of its routing table to its directly attached neighbors. This is a periodic advertisement, meaning that even if there have been no topological changes, a distance-vector routing protocol will, at regular intervals, advertise again its full routing table to its neighbors.
Another drawback to distance-vector routing protocols is the time they take to converge, which is the time required for all routers to update their routing table in response to a topological change in a network.
Hold-down timers can speed the convergence process. After a router makes a change to a route entry, a hold-down timer prevents any subsequent updates for a specified period of time. This approach helps stop flapping routes (which are routes that oscillate between being available and unavailable) from preventing convergence.
Yet another issue with distance-vector routing protocols is the potential of a routing loop. hop count, which is the number of routers that must be crossed to reach a network.
Split horizon: The split-horizon feature prevents a route learned on one interface from being advertised back out of that same interface. Poison reverse: The poison-reverse feature causes a route received on one interface to be advertised back out of that same interface with a metric considered to be infinite.
*** link-state routing protocol allows routers to build a topological map of the network.
distance-vector routing protocols
Routers send link-state advertisements (LSAs) to advertise the networks they know how to reach. Routers then use those LSAs to construct the topological map of a network. link-state routing protocols exchange full routing information only when two routers initially form their adjacency. Then routing updates are sent in response to changes in the network, as opposed to being sent periodically. Also, link-state routing protocols benefit from shorter convergence times, as compared to distance-vector routing protocols.
LSAs
Routing Information Protocol (RIP): A distance-vector routing protocol that uses a metric of hop count. The maximum number of hops between two routers in an RIP-based network is 15. Therefore, a hop count of 16 is considered to be infinite. Also, RIP is an IGP.
RIP
