barcode vb.net 2013 Figure 8-9 Example of a tunnel between two firewalls in Objective-C

Encoder QR-Code in Objective-C Figure 8-9 Example of a tunnel between two firewalls

Figure 8-9 Example of a tunnel between two firewalls
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IPv6 header (src=H1, dest=H2, Next Header=TCP)
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Figure 8-10 IPv6 packet sent from H1 to FW1
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TCP payload
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IPv6 header (src=FW1, dest=FW2, Next Header=AH)
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Figure 8-11 IPv6 packet sent from FW1 to FW2
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AH header (Next Header=IPv6) IPv6 header (src=H1, dest=H2, Next Header=TCP) TCP payload
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can be deleted by intermediate nodes or recorded and later replayed These attacks cannot be easily contrasted at the IP level; appropriate defenses (such as the use of unique packet identifiers and the generation of heartbeat packets) are usually placed at some upper level in the network stack A partial solution at the IP level is likely to be offered by the new format and algorithms that are going to replace the current ones in the AH header Comparing this method of creating a VPN with the one usually adopted in IPv4 by many firewall suppliers that also offer secure tunnels is interesting The basic architecture is the same as that used in IPv6 (refer to Figure 8-9), but, because IPv4 does not allow for multiple headers, the tunnel has to be implemented by some form of encapsulation, such as IP in IP15 Obviously, this solution raises problems of compatibility between the firewalls of different vendors as well as fragmentation problems If the packet to be transmitted already has the maximum dimension allowed for an IP packet, then encapsulating it inside another IP packet is not possible; fragmentation and reassembling must take place at the two endpoints of the tunnel As a consequence, the performance of the virtual channel can degrade down to 50 percent of the normal throughput The worst case takes place for larger packets, which are typically used in transferring large data sets that, by contrast, would need no fragmentation to achieve maximum speed On the other hand, the best case occurs for small packets, such as those used in interactive applications that, ironically, would better accept even a larger performance penalty, as long as the total throughput remains compatible with the reaction time of the human operator In IPv6, the situation is completely inverted; because the overhead is fixed in size (the dimension of AH, or that of AH plus ESP) and independent of the dimension of the original packet, the applications that suffer the highest overhead are the interactive ones, which are the applications with better resistance properties Anyway, in both cases, the performance penalty is definitely lower for the VPN implemented in IPv6 compared to those built in IPv4 Last but not least, it is interesting to realize that this VPN technique can be adopted even between a firewall and a single external host (see Figure 8-13) Obviously, this case is of particular relevance to guaranteed security when a mobile host is used outside the protected network perimeter, and it is a perfect complement to the mobility support features of IPv6 (see 10) The firewall will act as home agent for HM in the Neigh-
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Figure 8-12
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IPv6 packet sent from FW2 to H2
IPv6 header (src=H1, dest=H2, Next Header=TCP) TCP payload
Security Features of IPv6
Figure 8-13 Tunnel between a firewall and a single host
bor Discovery procedure HM will be assigned two different IP addresses: one when it is connected inside the security perimeter and the other one when it is outside the perimeter In this last case, the firewall will also act as a relay, by redirecting packets coming from inside the corporate network to the external address, after adding the required headers (AH only, or AH plus ESP)
Application-Level Security
Networked applications executing on top of an IPv6 stack may choose to require the use of a communication channel with specific features To avoid duplication of functionality (and hence performance degradation), being able to specify, at the transport layer, the security attributes of the channel being created is useful In the first BSD-UNIX implementations of IPv6, this effect can be obtained by properly using the setsocketoption() system call Anyway, this solution is not complete for application-level security because only partial protection is obtained AH provides host-based authentication only; whereas applications usually require user-based authentication Moreover, AH and ESP protect the data only during their transmission along the channel After the data have been received, they are no longer protected in any way This fact may not be relevant if the receiving host is a secure one, but there is the additional implication that origin authentication and data integrity properties are lost as well, so formal nonrepudiation cannot occur after the data have been extracted from the secure channel We can therefore draw the conclusion that the security features of IPv6 do not eliminate the need for other security mechanisms, which will probably be better placed at the application level
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