P2. Modules 7-9 Available and Reliable Networks Flashcards
What is Dynamic Host Configuration Protocol v4? (DHCPv4)
Its a protocol which assigns Ipv4 addresses, subnet mask, default gateway and a DNS server( translating domain names to numeric ip address)
What is a DHCP server lease? explain the process of leasing.
A DHCP server lease is a process in which a server leases from a pool of Ipv4 addresses for a limited period(24hrs or week) or until the client doesn’t need it anymore, after the lease expires, the client can ask for another address(normally same address)
1
DHCP Discover, Discovers available DHCPv4 servers with MAC address
2
DHCP Offer, When the server receiver the discover message, it reserves an available ipv4 address.
3
DHCP Request, When the client receives the offer from the server, it sends back a request message, it servers as a binding acceptance notice to the selected server.
4
DHCP Acknowledgment, On receiving the DHCPRequest message, the server may verify the lease information with an ICMP ping to that address to ensure it is not being used already
How do you renew a lease?
- Send DHCP request because we already are in contact with the server. If a DHCPACK is not received within a specified amount of time, the client broadcasts another DHCPREQUEST sot aht one of the other DHCPv4 servers can extend the lease.
- DHCP Acknowledgment (DHCPACK). On receiving the DHCPREQEUST message, the server verifies the lease information by returning a DHCPACK.
How is an Ipv6 GUA address manually configred on a router?
On a router, an IPv6 global unicast address (GUA) is manually configured using the ipv6 address ipv6-address/prefix-length interface configuration command.
What are RA message flags? Which types do we have?
RA message flags identifies the dynamic options available to a host
A flag - This is the Address Autoconfiguration flag. Use Stateless Address Autoconfiguration (SLAAC) to create an IPv6 GUA
O flag - This is the Other Configuration flag. Other information is available from a stateless DHCPv6 server.
M flag - This is the Managed Address Configuration flag. Use a stateful DHCPv6 server to obtain an IPv6 GUA.
What is SLAAC? How does it work?
SLAAC method enables hosts to create their own unique Ipv6 global unicast address without the services of a DHCPv6 server which means it is stateless.
SLAAC sends periodic RA (Router acknowledgment) messages (200sec) providing addressing and other config infor for hosts to auto-config themselves.
Hosts can also get these by sending a RS message (Router Solicidiation)
What is SLAAC DAD (DUPLICATE ADDRESS DETECTION)?
DAD checks if there are any of the same ip addresses.
It works by sending an ICMPv6 NS (neigbourt solicidation) message with a specially constructed solicited-node multicast address containing the last 24 bits of IPv6 address of the host.
If no ther devices respons with a NA (neighbour advertisement) message, the address is unique. If no NA is received, the address it no unique.
Not really required cause there is 18 quintillion posibilites.
Stateful DHCPv6
Compared to SLAAC which is stateless(no server), we have stateful which utilizes a DHCPv6 server to keep track of the allocated IP address bindings using a list.
How does a client get an Ipv6 address through DHCPv6?
- Host sends a Router Solicidation message(RS)
- Router responds with Router Acknowledgment message(RA)
- Hosts sends a DHCPv6 SOLICIT message.
- The DHCPv6 server responds with an ADVERTISE message
- Host responds to DHCPv6 server
- DHCPv6 server sends a REPLY message
Why do we have FHRPs?
Whenever a router interface that servers as a default gateway fails, the hosts| configured with that default gateway are isolated from outside networks.
FHRP is a mechanism used to provide alternate default gateways in switched networks where two or more routers are connected to the same VLAN.
What is router redundancy?
To prevent a single point of failure at default GW, we can implement a virtual router (VR)
By Sharing an IP and MAC address, two or more routers can act as a single VR, VR
What is Hot Standby Router Protocol (HSRP)? How does the priority work and what happends if the old active works again?
Designed to allow for transparent failover of a first hop Ipv4/Ipv6 device, standby router monitors the status of the HSrip group and to assume packet forwarding if active router fails.
Defines a group of routers - one active and one standby; virtual IP and MAC address are shared between
the two. And whenever the active fails, the router with the highest HSRP priority become the new active router and new default gateway, if they are the same priority, it is the router with the numerically highest ipv4 address. (range is from 0-255)
If the old active router starts working again, the new active router will remain the active router even if another router comes online with a higher HSRP priority.
We will then need to use preemption, it will trigger a new re-election process.
What is Virtual Router Redundancy Protocol v2? (VRRP v2)
One router is elected as the virtual router master, with the other routers acting as backups, in case the virtual router master fails.
Gateway Load Balancing Protocol (GLBP)
Protects data traffic from a failed router or circuit allowing load balancing between a group of redundant routers. No GLBP for Ipv6
How long does it take for the standby router to take the now inactive routers “place” after it stopped working.
The active and standby HSRP routers send hello packets to the HSRP group multicast address every 3 seconds by default. The standby rouiter will become active if it does not receive a hello message from the active rouer after 10 seconds .
