1 00:00:00,630 --> 00:00:04,500 So what is a PvP plus or rapid pvp plus? 2 00:00:04,500 --> 00:00:10,320 Extended bridge id now spanning tree requires that every switch have a unique bridge ID. 3 00:00:10,650 --> 00:00:16,170 In the past there's simply consisted of the bridge priority and Mac address. 4 00:00:16,470 --> 00:00:23,700 So bridge ID consists of eight bytes with two bytes being the bridge priority and six points being the 5 00:00:23,700 --> 00:00:24,660 MAC address. 6 00:00:25,080 --> 00:00:31,770 However, when configuring multiple VLANs and running per VLAN spanning tree, a different Mac address 7 00:00:31,770 --> 00:00:35,660 would have to be allocated for every VLAN PVS. 8 00:00:35,670 --> 00:00:39,450 RT creates an instance on a per VLAN basis. 9 00:00:39,570 --> 00:00:46,530 So to ensure that the bridge ID is unique on a per VLAN basis, a different MAC address would have to 10 00:00:46,530 --> 00:00:47,490 be allocated. 11 00:00:47,910 --> 00:00:54,810 Now that works fine if you only have a few VLANs, but if you configuring hundreds or thousands of VLANs, 12 00:00:54,810 --> 00:00:56,340 it's not scalable. 13 00:00:56,490 --> 00:01:03,120 If a vendor was supporting PVS, DT, the vendor would need to assign a unique Mac address on a per 14 00:01:03,120 --> 00:01:04,379 VLAN basis. 15 00:01:05,010 --> 00:01:13,230 So in theory, if 4094 VLANs were supported on a switch, 4094 unique Mac addresses would need to be 16 00:01:13,230 --> 00:01:15,450 assigned to every switch. 17 00:01:15,630 --> 00:01:17,760 That's simply not scalable. 18 00:01:17,910 --> 00:01:25,260 So to conserve Mac addresses, the system was changed and an extended system ID is also known as MAC 19 00:01:25,260 --> 00:01:26,430 address reduction. 20 00:01:26,820 --> 00:01:33,990 So with extended bridge IDs, the bridge ID is still eight bytes in size, but the priority is now split 21 00:01:33,990 --> 00:01:35,370 into two parts. 22 00:01:35,700 --> 00:01:44,700 So the two byte priority portion consists of a four bit bridge priority and a 12 but extended system 23 00:01:44,700 --> 00:01:45,330 ID. 24 00:01:45,660 --> 00:01:48,900 The MAC address is still six bytes in size. 25 00:01:49,920 --> 00:01:52,950 So please note bridge priority is for bits. 26 00:01:53,250 --> 00:01:57,630 Extended system ID is 12 bits, which equates to two bytes. 27 00:01:58,020 --> 00:02:04,290 The extended system ID is populated with the VLAN number and the bridge priority is a value that you 28 00:02:04,290 --> 00:02:05,100 can set. 29 00:02:05,430 --> 00:02:08,759 Default is 32768 in decimal. 30 00:02:09,360 --> 00:02:15,570 In the past the bridge priority consisted of two bytes and you could set the priority to a value such 31 00:02:15,570 --> 00:02:16,290 as one. 32 00:02:16,410 --> 00:02:19,630 However, that's no longer supported on a switch. 33 00:02:19,650 --> 00:02:30,000 As an example, if I type spanning tree VLAN one priority and try and set it to one, I'm told that 34 00:02:30,000 --> 00:02:36,600 I need to set it in increments of 4096 so the values allowed are one of these. 35 00:02:37,140 --> 00:02:44,040 The reason for that is that the bridge property has been split into two portions with only the most 36 00:02:44,040 --> 00:02:48,180 significant four bits being available for the priority. 37 00:02:48,390 --> 00:02:56,190 So if you set the bridge priority portion the four bits to binary one and you take the full two bytes 38 00:02:56,190 --> 00:03:00,540 into account, that would equate to 4096 in decimal. 39 00:03:00,810 --> 00:03:08,440 So if the priority bit is set to one, the extended bridge ID priority works out to 4096. 40 00:03:08,460 --> 00:03:17,280 If you take into account the full two bytes, if you set the bridge priority portion to two, so 0010 41 00:03:17,280 --> 00:03:24,420 in binary and look at the full 16 bits or two bytes, it equates to 8192 in decimal. 42 00:03:24,720 --> 00:03:30,480 On some vendor's equipment, you can set the priority to one and it will automatically be converted 43 00:03:30,480 --> 00:03:32,010 to 8192. 44 00:03:32,100 --> 00:03:38,220 But on Cisco switches, you need to set the bridge priority in multiples of 4096. 45 00:03:38,970 --> 00:03:43,260 So once again, if I try and set the priority to one, it's not allowed. 46 00:03:43,680 --> 00:03:45,750 Set it to 4000 and. 47 00:03:46,660 --> 00:03:47,660 96. 48 00:03:47,680 --> 00:03:50,770 That's allowed to show spanning tree. 49 00:03:51,160 --> 00:03:58,240 Notice the property of the switch because it's running PV plus it's 4097. 50 00:03:58,390 --> 00:04:05,560 So the priority plus the VLAN number, if you were looking at VLAN ten as an example, the priority 51 00:04:05,560 --> 00:04:08,440 would be 4096 plus ten. 52 00:04:08,590 --> 00:04:13,390 If you're looking at VLAN 20, it would be 4096 plus 20. 53 00:04:13,600 --> 00:04:15,940 I'll demonstrate that in a separate video. 54 00:04:17,390 --> 00:04:24,050 Now over the years, various enhancements have been made to spanning tree to reduce convergence time. 55 00:04:24,530 --> 00:04:30,170 So in a switched environment, various enhancements have been made to the protocol to make sure that 56 00:04:30,170 --> 00:04:31,520 things happen quicker. 57 00:04:31,880 --> 00:04:37,730 A standard port on a switch could take 30 seconds to converge, and that's not acceptable in modern 58 00:04:37,730 --> 00:04:38,750 day networks. 59 00:04:38,870 --> 00:04:45,530 As an example, if the PC was booting up and needed to connect to a DHCP server, the PC would boot 60 00:04:45,530 --> 00:04:50,820 up and send out a DHCP request before the switch port is converged. 61 00:04:50,840 --> 00:04:57,410 So the PC would have already booted up and requested an IP address before 30 seconds have expired and 62 00:04:57,410 --> 00:05:04,130 hence the PC wouldn't receive an IP address from the DHCP server because the DHCP request from the PC 63 00:05:04,130 --> 00:05:09,290 would be dropped by this port which is blocking while it's converging. 64 00:05:09,470 --> 00:05:13,340 So to improve performance in switched environments. 65 00:05:13,520 --> 00:05:21,320 Edge ports, in other words, ports connected to edge devices such as PCs, some servers and routers 66 00:05:21,320 --> 00:05:28,340 would be configured as Port First ports in a Cisco environment or as edge ports on other vendor equipment. 67 00:05:29,720 --> 00:05:31,940 Cisco used the term port first. 68 00:05:31,970 --> 00:05:34,580 Other vendors use the term edge ports. 69 00:05:34,820 --> 00:05:41,090 In some terminology, Cisco will use the term port first, and in other terminology it will be referred 70 00:05:41,090 --> 00:05:42,590 to as an edge port. 71 00:05:42,890 --> 00:05:49,280 Now it's important that you only enable port first ports on access ports and not on trunk ports. 72 00:05:49,670 --> 00:05:56,210 In other words, you shouldn't enable port first on links between switches because that will introduce 73 00:05:56,210 --> 00:05:57,770 loops in your topology. 74 00:05:58,070 --> 00:06:05,060 An edge port or a port first port immediately transitions to the forwarding state, so it bypasses the 75 00:06:05,060 --> 00:06:06,950 listening and learning states. 76 00:06:07,160 --> 00:06:14,060 It goes directly from blocking to forwarding, once again skipping both listening and learning states. 77 00:06:14,330 --> 00:06:19,340 That allows for much quicker convergence because rather than waiting for spelling tree to go through 78 00:06:19,340 --> 00:06:25,220 various stages such as blocking, listening, learning, forwarding the port just starts immediately 79 00:06:25,220 --> 00:06:28,550 forwarding traffic and hence convergence is a lot quicker. 80 00:06:29,440 --> 00:06:34,110 Spending trees still running on that port, but transitions immediately to forwarding. 81 00:06:34,120 --> 00:06:40,750 So if for some reason a BPD view was received on the port, the port can go back to the blocking state. 82 00:06:41,050 --> 00:06:47,560 It's good practice to do this because you don't want to inadvertently introduce loops because someone 83 00:06:47,560 --> 00:06:51,670 plugged in a switch as an example by mistake on a port first port.