2017 on Ricky

Representative HTTP Status Codes

Fri, 15 Dec 2017 15:33:14 +0800

Representative HTTP Status Codes

Switch notes

Sat, 25 Nov 2017 11:47:37 +0800

Switch

Switches are usually L2 devices

They forward packets only to the destination host (based on the MAC table), which reduces collisions and eavesdropping. Switches can also handle packets arriving at the same time, while hubs cannot.

Hubs are L1 devices

They forward packets from any host to all connected hosts, so collisions happen and cause random retries.

MAC Table

Learning
- A packet arrives on some port (network A) from MAC X destined for MAC Y. The switch records that MAC X is on network A. This is called learning.
Flooding
- The switch does not yet know where MAC Y is, so it forwards the packet to all networks except A. This is called flooding.
Forwarding
- The host with MAC Y receives the packet and sends an ACK to MAC X. The switch records that MAC Y is on that network, then forwards the ACK to MAC X. This is forwarding.
Filtering
- The switch receives a packet and finds that the source and destination MACs are on the same network, so it drops the packet. This is filtering.
Aging
- Each MAC-table entry has a timestamp of last access. Entries older than a threshold (configurable) are removed. This is aging.

Vlan

Switch interfaces must support 802.1Q

Juniper notes

Thu, 23 Nov 2017 16:00:00 +0800

[Juniper Firewall] tunnel

ACG icare@TWCHIJF01# show | compare rollback 4

[edit security policies]
 from-zone DB_12 to-zone TCT_Office { ... }
+ from-zone DB_12 to-zone JC32 {
+ policy For_Backup {
+ match {
+ source-address DB_10.11.12.0/24;
+ destination-address BACKUP_10.32.32.130;
+ application any;
+ }
+ then {
+ permit;
+ }
+ }
+ }
[edit security zones security-zone DB_12 address-book]
 address DB_10.11.12.57 { ... }
+ address DB_10.11.12.0/24 10.11.12.0/24;
[edit security zones]
 security-zone ESB_15 { ... }
+ security-zone JC32 {
+ address-book {
+ address BACKUP_10.32.32.130 10.32.32.130/32;
+ }
+ host-inbound-traffic {
+ system-services {
+ ping;
+ }
+ }
+ interfaces {
+ gr-0/0/0.32;
+ }
+ }
[edit interfaces gr-0/0/0]
+ unit 32 {
+ description To_JC32_DBBackup;
+ tunnel {
+ source 202.168.193.128;
+ destination 218.253.210.8;
+ }
+ family inet {
+ address 10.32.0.101/30;
+ }
+ }
[edit routing-options static]
 route 0.0.0.0/0 { ... }
+ route 10.32.32.130/32 next-hop 10.32.0.102;

set security policies from-zone DB_12 to-zone JC32 policy For_Backup match source-address DB_10.11.12.0/24
set security policies from-zone DB_12 to-zone JC32 policy For_Backup match destination-address BACKUP_10.32.32.130
set security policies from-zone DB_12 to-zone JC32 policy For_Backup match application any
set security policies from-zone DB_12 to-zone JC32 policy For_Backup then permit
set security zones security-zone DB_12 address-book address DB_10.11.12.0/24 10.11.12.0/24
set security zones security-zone JC32 address-book address BACKUP_10.32.32.130 10.32.32.130/32
set security zones security-zone JC32 host-inbound-traffic system-services ping
set security zones security-zone JC32 interfaces gr-0/0/0.32
set interfaces gr-0/0/0 unit 32 description To_JC32_DBBackup
set interfaces gr-0/0/0 unit 32 tunnel source 202.168.193.128
set interfaces gr-0/0/0 unit 32 tunnel destination 218.253.210.8
set interfaces gr-0/0/0 unit 32 family inet address 10.32.0.101/30
set routing-options static route 10.32.32.130/32 next-hop 10.32.0.102

icare@TWCHIJF01> show configuration | compare rollback 1

Data Center Notes

Tue, 24 Oct 2017 23:17:33 +0800

First NIC - blue cable

Second NIC - green cable

Switch interconnect - white cable

Yellow, red

Storage has disk arrays and heavy data transfer, so it uses fiber connections and fiber switches.

Fiber colors:

Multi-mode or single-mode fiber

Single-mode fiber is yellow. Multi-mode fiber (50μm or 62.5μm) is usually orange. 10GB multi-mode fiber is usually aqua.

Common spec distinctions:

OS1, OS2, 9µm, 9/125 = single-mode fiber
OM1, 62.5µm, 62.5/125 = 62.5 multi-mode fiber
OM2, 50µ, 50/125 = 50 multi-mode fiber
OM3, 10GB, 50µm, 50/125 = 10GB multi-mode fiber
OM4, 100GB, 50µm, 50/125 = 100GB multi-mode fiber

Fiber structure

Route notes

Sat, 16 Sep 2017 15:00:00 +0800

Router - a device that is good at computing routing tables, an L3 device.

Routing Table

A NIC with one IP naturally has two routes and they cannot be changed. 192.168.1.1/24
- Itself. Local route / Host route: 192.168.1.1/32
- The whole subnet. Direct route / Connect route: 192.168.1.0/24
You can add as many static routes as you want.
- 172.10.10.10/24 -> 192.168.1.2
- 2.2.2.2/26 -> 192.168.1.9
- …
Default route - only one gateway.
- 0.0.0.0/0 -> 192.168.1.10
More specific routes take precedence.
BGPv4

Arp notes

Sun, 03 Sep 2017 15:00:00 +0800

Before a packet is sent

Look up the MAC for the IP in the ARP table
- MAC found - encapsulate
- No MAC - broadcast
  - Same subnet - OK
  - Different subnet - look up the router MAC in the ARP table
    - Found - OK
    - Not found - broadcast