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ISCW - GRE/Availability IPsec
ISCW - GRE/Availability IPsec
26
Education
Graduate
07/31/2008

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Term
How many additional bytes of overhead are added to a packet when using GRE?
Definition
GRE adds an additional 24-byte header of overhead. This overhead contains a new 20-byte IP header, which indicates the source and destination IP addresses of the GRE tunnel. The remaining 4 bytes are the GRE header itself.
Term
What command defines the local tunnel interface (source interface)?
Definition
tunnel source interface
Term
What command configured the tunnel destination when configuring a GRE tunnel?
Definition
tunnel destination ip-address
Term
What command sets the encapsulation mode for the tunnel interface?
Definition
tunnel mode {gre | ipip | iptalk | mpls| ipsec}
Term
What command associates a tunnel interface with an IPsec profile?
Definition
tunnel protection ipsec profile profile-name
Term
Describe how dead peer detection (DPD) is used with an IPsec VPN setup.
Definition
DPD offers a stateless failover from on VPN tunnel to another. This means that the routers are not keeping track of which VPN tunnels are currently live. Instead, traffic flows through the primary tunnel until it fails, at which time a secondary tunnel is selected.
Term
What are the different modes that dead peer detection can run in?
Definition
DPD can run in either periodic mode or on-demand mode.
Term
Describe the general characteristics of Dead Peer Detection's (DPD) periodic mode.
Definition
DPD periodic mode sends keepalive messages periodically between IPsec VPN peers. These messages are in addition to the normal IPsec rekey messages. Also, the messages are not sent if user data is transmitted through the VPN tunnel, and are only used when there is a lull in tunnel traffic.
Term
Describe the general characteristics of Dead Peer Detection's (DPD) on-demand mode.
Definition
DPD on-demand is the defaul mode on Cisco IOS devices. The keepalive messages are sent only if the liveliness of the remote peer is in question. Like in periodic mode, messages are never sent during otherwise idle tunnel moments.
Term
What command determines the mode and frequency of Dead Peer Detection (DPD)?
Definition
crypto isakmp keepalive seconds [retries] [periodic | on-demand]
Term
What command set the peer for a VPN IPsec tunnel?
Definition
set peer ip-address [default]
Term
What are the 2 protocols used to maintain IPsec stateful failover?
Definition

- HSRP - Monitors both the inside and outside interfaces. If either goes down, the entire router is deemed unworthy and ownership of the IKE and IPsec SA processes is passed to the standby router.

 

- Stateful Switchover (SSO) - Shares the IKE and IPsec SA information between the active and backup routers. At any time, either router knows enough to be the active IPsec VPN router.

Term
What command configures redundancy and enters inter-device configuration mode?
Definition
redundancy inter-device
Term
What command initiates the communication link between active and standby routers?
Definition
ipc zone default
Term
Describe the basic configuration of Stream Control Transmission Protocol (SCTP) for device redundancy.
Definition
Within SCTP, the local and remote SCTP ports and the IP addresses are defined. The local port defined on this router must match the remote port on the peer router. Also, the local IP and remote IP addresses should point to physical interface IP addresses and not to a virtual IP address.
Term
What command defines the number of SCTP retries before an attempt to create an SCTP session fails?
Definition
path-retransmit retries
Term
What command defines the maximum amount of time that SCTP waits before retransmitting data?
Definition
retransmit-timeout seconds
Term
What command defines the HSRP group that provides redundancy for a crypto map?
Definition
crypto map map-name redundancy group-name [stateful]
Term
What command is use to configure a preshared authentication key?
Definition
crypto isakmp key keystring {address address | host host}
Term
What command names the redundancy scheme used between 2 devices?
Definition
scheme standby group-name
Term
What command creates the association between 2 devices when using the interdevice communication protocol (ICP)?
Definition
association group
Term
What command configures Stream Control Transmission Protocol (SCTP)?
Definition
protocol sctp
Term
What command defines the local SCTP port number used to communicate with the redundant peer?
Definition
local-port port-number
Term
What command defines a local IP to communicate with a redundant peer?
Definition
local-ip ip-address
Term
What command defines the remote SCTP port number used to communicate with the redundant peer?
Definition
remote-port port-number
Term
What command defines the remote IP to communicate with the peer?
Definition
remote-ip ip-address
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