You must create an IP-IP tunnel between two routers on your network. These two devices are separated by 10 hops. The tunnel appears to be established, but no traffic is traversing the tunnel.
What causes this behavior?
A.
The tunnel’s TTL has not been modified from the default value of 8.
B.
Traffic is being dropped along the path because a configured MTU is greater than the tunnel’s MTU.
C.
A route that directs traffic into the tunnel is not present.
D.
BGP has not been enabled between tunnel end-points.
Explanation:
The ERX system supports static IP tunnels. An IP tunnel is a virtual point-to-point connection between two routers. See Figure 4-1. To establish an IP tunnel, you specify a tunnel type and name, and then configure an interface on each router to act as an endpoint for the tunnel.The ERX system supports the following types of IP tunnels:
Generic Routing Protocol (GRE) tunnels
Distance Vector Multicast Routing Protocol (DVMRP) tunnels, also
known as IP in IP tunnelsIP Tunneling (Generic Routing Encapsulation)
GRE (Generic Routing Encapsulation) or IP tunneling (IP encapsulation) is a technique that encapsulates IP datagrams within IP datagrams. GRE is a technique that allows datagrams to be encapsulated into IP packets and then redirected to an intermediate host. At this intermediate destination, the datagrams are decapsulated and then routed to the next leg. In doing so, the trip to the intermediate host appears to the inner datagrams as one hop. The general outline of GRE can be found in RFC 1701.
An IP tunnel is an Internet Protocol (IP) network communications channel between two networks. It is used to transport another network protocol by encapsulation of its packets.
IP tunnels are often used for connecting two disjoint IP networks that don’t have a native routing path to each other, via an underlying routable protocol across an intermediate transport network. In conjunction with the IPsec protocol they may be used to create a virtual private network between two or more private networks across a public network such as the Internet. Another prominent use is to connect islands of IPv6 installations across the IPv4 Internet.IP tunnelling encapsulation
In IP tunnelling, every IP packet, including addressing information of its source and destination IP networks, is encapsulated within another packet format native to the transit network.
At the borders between the source network and the transit network, as well as the transit network and the destination network, gateways are used that establish the end-points of the IP tunnel across the transit network. Thus, the IP tunnel endpoints become native IP routers that establish a standard IP route between the source and destination networks. Packets traversing these end-points from the transit network are stripped from their transit frame format headers and trailers used in the tunnelling protocol and thus converted into native IP format and injected into the IP stack of the tunnel endpoints. In addition, any other protocol encapsulations used during transit, such as IPsec or Transport Layer Security, are removed.
IP in IP, sometimes called ipencap, is an example of IP encapsulation within IP and is described in RFC 2003. Other variants of the IP-in-IP variety are IPv6-in-IPv4 (6in4) and IPv4-in-IPv6 (4in6).
IP tunneling often bypasses simple firewall rules transparently since the specific nature and addressing of the original datagrams are hidden. Content-control software is usually required to block IP tunnels.
Useful links:
http://www.juniper.net/techpubs/software/erx/erx41x/swconfig-routing-vol1/download/ip-tunnels-config.pdf
http://www.qnx.com/developers/docs/6.4.0/neutrino/technotes/gre.html
