Chap 1 - IPv4-IPV6 Addressing and Routing Flashcards
What is DORA?
- DHCP message sequence for IPv4
- Discover
- Offer
- Request
- Acknowledgement
What 7 other protocols are forwarded by the ip helper-address command?
- TFTP
- Domain Name System (DNS)
- Internet Time Service (ITS)
- NetBIOS name server
- NetBIOS datagram server
- BootP
- TACACS
What are 8 DHCP message types?
- DHCPREQUEST
- DHCPDECLINE
- DHCPACK
- DHCPNAK
- DHCPRELEASE
- DHCPINFORM
Who sends the DHCPDECLINE message and what does it do?
This message is sent from a client to a DHCP server to inform the server that an IP address is already in use on the network.
Who sends the DHCPNAK message and what does it do?
- Sent from server to client
- Says server is declining to provide IP address information to the client
Who sends the DHCPINFORM message and what does it do?
- Sent from a client to a DHCP server
- It requests IP configuration parameters. Such a message might be sent from an access server requesting IP configuration information for a remote client attaching to the access server.
What command enables an IP router to function as a DHCP client?
Interface command “R1(config-if)# ip address dhcp”
What is APIPA ?
- Automatic Private IP Addressing address
- 169.254.x.x
What should you not assume if a client gets an APIPA address?
Don’t automatically assume it is a DHCP issue. It could also mean there’s a layer 2 problem.
What are 7 potential issues when troubleshooting a DHCP problem?
* Router not forwarding broadcasts * DHCP pool out of addresses * Misconfiguration * Duplicate IP addresses * Redundant DHCP servers not communicating * The pull nature of DHCP - server cannot push an address to a client * Interface not configured with IP address in DHCP pool
What show command do you use to check for duplicate IP addresses
show ip dhcp conflict
What command is used to clear a conflict ?
clear ip dhcp conflict *
What command allows you to see assigned DHCP addresses
show ip dhcp binding
What command is used to clear a binding?
clear ip dhcp binding *
What debug command can be used to view updates to the DHCP database?
debug ip dhcp server events
What debug command can be used to view DORA ?
debug ip dhcp server packets
On a Windows machine what command will show the IPV6 address?
ipconfig
What does an entry ending in 11% mean on a Windows PC?
It indicates which interface packets will be sent out of.
What are 3 ways an end station can get its IPV6 host address?
- Statically assigned
- Automatically assigned randomly
- Assigned based on EUI-64
How is an EUI-64 address computed?
- Split the MAC address in half
- Insert FFFE
- Flip the 7th bit from the left (1 becomes 0, or 0 becomes 1)
What does a link local address start with?
FE80:
By default how do Windows machines calculate their IPV6 addresses?
Randomly using SLAAC
By default how do routers calculate their link local addresses?
Routers use EUI-64 to calculate their link local addresses
How do you get a router to use EUI-64 to configure its global unicast address?
R1(config-if)# ipv6 address 2001:db8:a:a::/64 eui-64
In IPV6 what are the 3 dynamic options for assigning addresses?
* SLAAC * Stateful DHCPv6 * Stateless DHCPv6
What does SLAAC stand for?
Stateless Autoconfiguration
What is the command to enable SLAAC on a router interface?
R1(config-if)# ipv6 address autoconfig
How does SLAAC work on a router?
* Router sends a Router Solicitation msg (RS) * Waits for another router on the same subnet to send Router Advertisement (RA) * Router derives the network prefix from the RA and then uses EUI-64 for the host identifier
How does SLAAC work on a PC?
* PC sends a Router Solicitation msg (RS) * Waits for a router on the same subnet to respond with a Router Advertisement (RA) * PC derives the network prefix from the RA and randomly computes its host identifier * PC uses the link local source address of the RA msg for its default gateway
When a router sends out an RA what are the L2 and L3 destination addresses?
* L3 destination address is FF02::1 (all nodes, link local multicast address) * L2 destination address is 33:33:00:00:00:01 (all nodes, link local multicast MAC address associated with FF02::1)
When a router sends out an RA what are the L2 and L3 source addresses?
* L3 source address is the router interface’s link local address * L2 source address is the MAC address of the interface the router used to send out the RA
What is the show command to verify a SLAAC generated address on a router?
show ipv6 interface
What would cause a router configured for SLAAC to use the source address of the RA as its default route?
If the SLAAC-configured router didn’t have ‘ipv6 unicast-routing’ enabled then it will act as a IPV6 client
What 3 conditions must be met before a router will send out RAs?
* ‘ipv6 unicast-routing’ global command configured * The physical interface must be enabled for IPV6 (R1(config-if)# ipv6 enable * RAs are not being surpressed on the interface
What show commands can you use to diagnose a router not sending RAs?
* show run | I ipv6 unicast-router * show ipv6 interface - look for ‘IPV6 is enabled’ and check for ‘ND RAs are suppressed (all)’
Users complaining they can get to some destinations but not all.
* Check for multiple gateways on the network * Verify that all gateways can get to all destinations
Users getting wrong IPV6 addresses.
Check the router or switch interface to make sure it is associated with the correct pool
What 2 things are required to implement Stateless DHCPv6?
* The router interface must have the following configured “R1(config-if)# ipv6 nd other-config-flag” * Interface needs a helper address R1(config-if)# ip dhcp relay
What is the DHCPv6 4-step negotiation process?
* SOLICIT * ADVERTISE * REQUEST * REPLY
In the ‘show ip route’ command what does the ‘longer-prefixes’ keyword do?
Shows networks that are subnets of the network being queries
When should you never add an outgoing interface in a static route?
When the outgoing network is ethernet
When do you HAVE to add an outgoing interface to a static route?
When running IPV6 and the next hop references the peer’s link local address.
