Installing Entware on Asus RT-AC88U, Asus RT-AC68U or Asus RT-AC87U .  Note, for this install, a USB drive is not required, however a USB drive is highly recommended.  However, these steps will dip into your /jffs space, so care should be taken to install just what you need, since space in /jffs is not unlimited. 

IMPORTANT: if using a USB flash storage, which is higly recommended, to have the USB drive mounted automagically on /opt, the LABEL on the disk must be set to Optware according to this howto for Entware.  Please use these steps to setup a USB drive to avoid the /jffs space limitations:

[root@rfc1178-01 ~]# mkfs.ext4 -L Optware /dev/sdd
mke2fs 1.42.7 (21-Jan-2013)
/dev/sdd is entire device, not just one partition!
Proceed anyway? (y,n) y
Filesystem label=Optware
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
1880480 inodes, 7511040 blocks
375552 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=0
230 block groups
32768 blocks per group, 32768 fragments per group
8176 inodes per group
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done   

[root@rfc1178-01 ~]# 
[root@rfc1178-01 ~]# 
[root@rfc1178-01 ~]# lsblk /dev/sdd
NAME MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdd    8:48   1 28.7G  0 disk 
[root@rfc1178-01 ~]# blkid /dev/sdd
/dev/sdd: LABEL="Optware" UUID="8ffab564-215e-4530-b00c-88813ef76122" TYPE="ext4" 
[root@rfc1178-01 ~]# 

If the volume is labeled correctly, it will auto mount as follows:

— /dev/sda
Block device, size 28.65 GiB (30765219840 bytes)
Ext4 file system
Volume name "Optware"
UUID 8FFAB564-215E-4530-B00C-88813EF76122 (DCE, v4)
Volume size 28.65 GiB (30765219840 bytes, 7511040 blocks of 4 KiB)
/dev/sda mounted to /opt

To start, our router model is:

CPU
CPU Model                        Broadcom BCM4709 
CPU Cores                        2 
CPU Features                     EDSP FASTMULT HALF TLS 
CPU Clock                        1400 MHz
Load Average                     0.08, 0.13, 0.07 %4
Temperatures                     CPU 78.6 °C / WL0 49.1 °C / WL1 50.0 °C

The broadcom link definining Broadcom BCM4707/4708/4709 however, has the following:

    1 GHz ARM® Cortex™-A9 dual-core with a 32 KB four-way set associative instruction cache, a 32 KB four-way set associative data cache and a 128-entry translation lookaside buffer (TLB).

Clearly showing it's ARM Cortex – A9 Dual Core CPU.  Status page confirms part of this above with the 2 cores.  So what package do we use for installnig Entware?  ARM based:

(Skip if USB storage used) mkdir /jffs/opt
(Skip if USB storage used) mount -o bind /jffs/opt /opt
cd /opt
wget http://bin.entware.net/armv7sf-k3.2/installer/generic.sh
chmod +x ./generic.sh; sh ./generic.sh

opkg update
opkg upgrade

At this point, Entware should be fully installed.  Run the following to list out and search for packages:

root@DD-WRT-ROMA:/opt# opkg list | grep -Ei netcat
ncat – 7.91-3 – Much-improved reimplementation of Netcat
netcat – 0.7.1-2 – Netcat is a featured networking utility which reads and writes data across network connections, using the TCP/IP protocol. It is designed to be a reliable "back-end" tool that can be used directly or easily driven by other programs and scripts. At the same time, it is a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities.
root@DD-WRT-ROMA:/opt#

Additional details can be found on the DD-WRT Entware page.  In case the above does NOT work, rules such as these may be required:

# ———————-
# ENTWARE – Cloud Flare Net IP Range used by: wget http://bin.entware.net/armv7sf-k3.2/Packages.gz
# ———————-
iptables -A INPUT -s 172.64.0.0/13 -d $(nvram get lan_ipaddr) -p udp –match multiport –sports 80,443 -j ACCEPT
iptables -A INPUT -s 172.64.0.0/13 -d $(nvram get lan_ipaddr) -p tcp –match multiport –sports 80,443 -j ACCEPT

iptables -A INPUT -s 172.64.0.0/13 -d $(nvram get wan_ipaddr) -p udp –match multiport –sports 80,443 -j ACCEPT
iptables -A INPUT -s 172.64.0.0/13 -d $(nvram get wan_ipaddr) -p tcp –match multiport –sports 80,443 -j ACCEPT

iptables -A INPUT -s 104.16.0.0/12 -d $(nvram get wan_ipaddr) -p udp –match multiport –sports 80,443 -j ACCEPT
iptables -A INPUT -s 104.16.0.0/12 -d $(nvram get wan_ipaddr) -p tcp –match multiport –sports 80,443 -j ACCEPT

Verify traffic using:

# tcpdump host 172.64.80.1 and port 80 -n -s 0 -vvv | tee -a tcpdump.log

Cheers,