On today's lab the following tripped me up: Task 32.6 - in this task we are asked to configure "Unique Local Addressing" (ULA) on the multipoint frame between R5/R7 that uses a randomly generated global ID. The 2nd and 3rd octets of the IPv4 address on this interface should be used to create the "subnet" portion of the ULA. We should also run RIPng on this link named cisco275
To answer this question we obviously need to understand the different types of IPv6 addresses. ULA is the successor to the old and deprecated site-local addresses. If you look this up in the RFC you will see that the ULA addresses fall into two ranges, FC00/8 and FD00/8. FC00/8 = ULA addresses that are centrally managed and allocated by registrars FD00/8 = ULA addresses that are not centrally managed and can be allocated by us the administrators http://tools.ietf.org/html/draft-ietf-ipv6-unique-local-addr-05 Since the FC00/8 is centrally managed I would assume that we are looking at using FD00/8, however how is the global ID randomly generated? If you read RFC1493 they've laid out a formula for generating these which you can see below. http://tools.ietf.org/html/rfc4193 3.2.2. Sample Code for Pseudo-Random Global ID Algorithm The algorithm described below is intended to be used for locally assigned Global IDs. In each case the resulting global ID will be used in the appropriate prefix as defined in Section 3.2. 1) Obtain the current time of day in 64-bit NTP format [NTP]. 2) Obtain an EUI-64 identifier from the system running this algorithm. If an EUI-64 does not exist, one can be created from a 48-bit MAC address as specified in [ADDARCH]. If an EUI-64 cannot be obtained or created, a suitably unique identifier, local to the node, should be used (e.g., system serial number). 3) Concatenate the time of day with the system-specific identifier in order to create a key. 4) Compute an SHA-1 digest on the key as specified in [FIPS, SHA1]; the resulting value is 160 bits. 5) Use the least significant 40 bits as the Global ID. 6) Concatenate FC00::/7, the L bit set to 1, and the 40-bit Global ID to create a Local IPv6 address prefix. This algorithm will result in a Global ID that is reasonably unique and can be used to create a locally assigned Local IPv6 address prefix. They say that the probability that two or more of these IDs will collide can be approximated using the formula: P = 1 - exp(-N**2 / 2**(L+1)) where P is the probability of collision, N is the number of interconnected Global IDs, and L is the length of the Global ID. But I digress... So we need to use FD00 - Now let's get back to the format of the address in the original question: FD00:0:0:xxxx::hostID The 2nd and 3rd octets of the IPv4 address on the multipoint interface are "100.25" 100 = 01100100 = 64 (hex) 25 = 00011001 = 19 (hex) ---------------------------- = 0x6419 FD00:0:0:6419::/64 what about the rest of the global ID? Does it matter? What about the host portion? (FD00:0:0:6419::2/64 OR FD00:0:0:6419::/64 eui-64) I opted out of eui-64 in favor of manually configuring the host portion using ::X where X is the router number (I verified and this matches the DSG as well)! Now according the RFC we should use eui-64, does this really matter for the CCIE lab? We obviously aren't going to use that method in the lab but thought it was interesting as to how they suggest we derive this information. Here are my configs from the task where I manually set the host portion to the router number (same as DSG) R2 interface Serial0/0/0.1 multipoint ipv6 address FD00:0:0:6419::2/64 ipv6 address fe80::2 link-local ipv6 rip cisco275 enable frame map ipv6 FD00:0:0:6419::2 215 frame map ipv6 FD00:0:0:6419::5 215 frame map ipv6 FE80::5 215 broadcast R5 ipv6 unicast-routing interface Serial0/0/0.1 multipoint ipv6 address FD00:0:0:6419::5/64 ipv6 address fe80::5 link-local ipv6 rip cisco275 enable frame map ipv6 FD00:0:0:6419::2 512 frame map ipv6 FD00:0:0:6419::5 512 frame map ipv6 FE80::2 512 broadcast UHS Confidentiality Notice: This e-mail message, including any attachments, is for the sole use of the intended recipient (s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution of this information is prohibited. If this was sent to you in error, please notify the sender by reply e-mail and destroy all copies of the original message. _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com
